Add a contributor guide

CONTRIBUTING.md

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+# Contributing to Obsidian Export
+
+Hi there!
+Thank you so much for wanting to contribute to this project.
+I greatly appreciate any efforts people like you put into making obsidian-export better!
+
+Managing an open-source project can take a lot of time and effort however.
+As this is a passion project which I maintain alongside my regular daytime job, I need to take some measures to safeguard my mental health and the enjoyment of this project.
+
+This document aims to provide guidance which makes contributions easier by:
+
+1. Defining the expectations I have of submissions to the codebase and the pull request process.
+2. Helping you get set up for development on the code.
+3. Providing pointers to some areas of the codebase, as well as some design considerations to take into account when making changes.
+
+## Working with Rust
+
+Obsidian-export is written in [Rust](https://www.rust-lang.org/), which is not the easiest of languages to master.
+If you'd like to contribute but you don't know Rust, check out [Learn Rust](https://www.rust-lang.org/learn) for some suggestions of how to get started with the language.
+In general, I will do my best to support you and help you out, but understand my time for mentoring is highly limited.
+
+To work on the codebase, you'll also need the Rust toolchain, including cargo, rustfmt and clippy.
+The easiest way is to [install Rust using rustup](https://www.rust-lang.org/tools/install), which lets you install rustfmt and clippy using `rustup component add rustfmt` and `rustup component add clippy` respectively.
+
+## Design principles
+
+My intention is to keep the core of `obsidian-export` as limited and small as possible, avoiding changes to the core [`Exporter`](https://docs.rs/obsidian-export/latest/obsidian_export/struct.Exporter.html) struct or any of its methods whenever possible.
+This improves long-term maintainability and makes investigation of bugs simpler.
+
+To keep the core of obsidian-export small while still supporting a wide range of use-cases, additional functionality should be pushed down into [postprocessors](https://docs.rs/obsidian-export/latest/obsidian_export/type.Postprocessor.html) as much as possible.
+You can see some examples of this in:
+
+- [Support Obsidian's "Strict line breaks" setting (#57)](https://github.com/zoni/obsidian-export/pull/57)
+- [Frontmatter based filtering (#67)](https://github.com/zoni/obsidian-export/pull/67)
+
+## Conventions
+
+Code is formatted with [rustfmt](https://github.com/rust-lang/rustfmt) using the default options.
+In addition, all default [clippy](https://github.com/rust-lang/rust-clippy) checks on the latest stable Rust compiler must also pass.
+Both of these are enforced through CI using GitHub actions.
+
+> **💡 Tip: install pre-commit hooks** 
+>
+> This codebase is set up with the [pre-commit framework](https://pre-commit.com/) to automatically run the appropriate checks locally whenever you commit.
+> Assuming you [have pre-commit installed](https://pre-commit.com/#install), all you need to do is run `pre-commit install` once to get this set up.
+
+Following my advice on [creating high-quality commits](https://nick.groenen.me/notes/high-quality-commits/) will make it easier for me to review changes.
+I don't insist on this, but pull requests which fail to adhere to these conventions are at risk of being squashed and having their commit messages rewritten when they are accepted.
+
+## Tests
+
+In order to have confidence that your changes work as intended, as well as to avoid regressions when making changes in the future, I would like to see code accompanied by test cases.
+
+At the moment, the test framework primary relies on high-level integration tests, all of which are defined in the [tests](tests/) directory.
+These rely on comparing Markdown notes [before](tests/testdata/input) and [after](tests/testdata/expected) running an export.
+By studying some of the existing tests, you should be able to copy and adapt these for your own changes.
+
+For an example of doing low-level unit tests, you can look at the end of [frontmatter.rs](src/frontmatter.rs).
+
+## Documentation
+
+I place a lot of value on good documentation and would encourage you to include updates to the docs with your changes.
+Changes or additions to public methods and attributes **must** come with proper documentation for a PR to be accepted.
+
+Advice on writing Rust documentation can be found in:
+
+- [The rustdoc book: How to write documentation](https://doc.rust-lang.org/rustdoc/how-to-write-documentation.html)
+- [Rust by example: Documentation](https://doc.rust-lang.org/rust-by-example/meta/doc.html)
+
+Updates to the user guide/README instructions are also preferred, but optional.
+If you don't feel comfortable writing user documentation, I will be happy to guide you or do it for you.
+
+> **⚠ Warning**
+>
+> If you update the README file, take note that you must edit the fragments in the [docs](docs/) directory as opposed to the README in the root of the repository, which is auto-generated.

README.md

@@ -243,6 +243,12 @@ All of the functionality exposed by the `obsidian-export` CLI command is also ac
 To get started, visit the library documentation on [obsidian_export](https://docs.rs/obsidian-export/latest/obsidian_export/) and [obsidian_export::Exporter](https://docs.rs/obsidian-export/latest/obsidian_export/struct.Exporter.html).
 
 
+# Contributing
+
+I will happily accept bug fixes as well as enhancements, as long as they align with the overall scope and vision of the project.
+Please see [CONTRIBUTING](CONTRIBUTING.md) for more information.
+
+
 # License
 
 Obsidian-export is dual-licensed under the [Apache 2.0] and the [MIT] licenses.

docs/CONTRIBUTING.md

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+../CONTRIBUTING.md

docs/_combined.md

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 ![[usage-basic]]
 ![[usage-advanced]]
 ![[usage-library]]
+![[contributing]]
 ![[license]]
 ![[CHANGES]]

docs/contributing.md

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+# Contributing
+
+I will happily accept bug fixes as well as enhancements, as long as they align with the overall scope and vision of the project.
+Please see [CONTRIBUTING](CONTRIBUTING.md) for more information.