Add CONTRIBUTING.md

Author: zecakeh

CONTRIBUTING.md

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+Welcome! Thanks for looking into contributing to our project!
+
+# Table of Contents
+
+- [Looking for Help?](#looking-for-help)
+  - [Documentation](#documentation)
+  - [Chat Rooms](#chat-rooms)
+- [Reporting Issues](#reporting-issues)
+- [Submitting Code](#submitting-code)
+  - [Coding Style](#coding-style)
+  - [Submitting PRs](#submitting-prs)
+  - [Where do I start?](#where-do-i-start)
+- [Testing](#testing)
+- [LLM Contributions](#llm-contributions)
+  - [Project-related use of LLMs](#project-related-use-of-llms)
+
+# Looking for Help?
+
+Here is a list of helpful resources you can consult:
+
+## Documentation
+
+- [Matrix spec Documentation](https://spec.matrix.org/latest/)
+
+## Chat Rooms
+
+- Ruma Matrix room: [#ruma:matrix.org](https://matrix.to/#/#ruma:matrix.org)
+- Ruma Development Matrix room: [#ruma-dev:matrix.org](https://matrix.to/#/#ruma-dev:matrix.org)
+- Matrix Developer room: [#matrix-dev:matrix.org](https://matrix.to/#/#matrix-dev:matrix.org)
+
+# Reporting Issues
+
+If you find any bugs, inconsistencies or other problems, feel free to submit
+a GitHub [issue](https://github.com/ruma/examples/issues/new).
+
+If you have a quick question, it may be easier to leave a message in
+[#ruma:matrix.org](https://matrix.to/#/#ruma:matrix.org).
+
+Also, if you have trouble getting on board, let us know so we can help future
+contributors to the project overcome that hurdle too.
+
+# Submitting Code
+
+Ready to write some code? Great! Here are some guidelines to follow to
+help you on your way:
+
+## Coding Style
+
+In general, try to replicate the coding style that is already present. Specifically:
+
+### Code Formatting and Linting
+
+We use [rustfmt] to ensure consistent formatting code and [clippy] to catch
+common mistakes not caught by the compiler as well as enforcing a few custom
+code style choices.
+
+```sh
+# if you don't have them installed, install or update the nightly toolchain
+rustup install nightly
+# … and install prebuilt rustfmt and clippy executables (available for most platforms)
+rustup component add rustfmt clippy
+```
+
+Before committing your changes, run `cargo +nightly fmt` to format the code (if
+your editor / IDE isn't set up to run it automatically) and
+`cargo +nightly clippy --workspace`¹ to run lints.
+
+¹ If you modified feature-gated code (`#[cfg(feature = "something")]`), you
+have to pass `--all-features` or `--features something` to clippy for it to
+check that code
+
+[rustfmt]: https://github.com/rust-lang/rustfmt#readme
+[clippy]: https://github.com/rust-lang/rust-clippy#readme
+
+### Import Formatting
+
+Organize your imports into three groups separated by blank lines:
+
+1. `std` imports
+1. External imports (from other crates)
+1. Local imports (`self::`, `super::`, `crate::` and things like `LocalEnum::*`)
+
+For example,
+
+```rust
+use std::collections::BTreeMap;
+
+use ruma_common::api::ruma_api;
+
+use super::MyType;
+```
+
+### Commit Messages
+
+The commit message should start with the _area_ that is affected by the change.
+An area is usually the name of the affected example. For example, the
+description of a commit that affects the hello_world example should look like
+"hello-world: Add new event".
+
+Write commit messages using the imperative mood, as if completing the sentence:
+"If applied, this commit will \_\_\_." For example, use "Fix some bug" instead
+of "Fixed some bug" or "Add a feature" instead of "Added a feature".
+
+(Take a look at this
+[blog post](https://www.freecodecamp.org/news/writing-good-commit-messages-a-practical-guide/)
+for more information on writing good commit messages.)
+
+## Submitting PRs
+
+Once you're ready to submit your code, create a pull request, and one of our
+maintainers will review it. Once your PR has passed review, a maintainer will
+merge the request and you're done! 🎉
+
+## Where do I start?
+
+If this is your first contribution to the project, we recommend taking a look
+at one of the [open issues][] we've marked for new contributors.
+
+[open issues]: https://github.com/ruma/examples/issues?q=is%3Aissue+is%3Aopen+label%3A"help+wanted"
+
+# Testing
+
+Before committing, run `cargo check` to make sure that your changes can build,
+as well as running the formatting and linting tools
+[mentioned above](#code-formatting-and-linting).
+
+# LLM Contributions
+
+Contributions must not include content generated by large language models
+or other probabilistic tools like ChatGPT, Claude, and Copilot.
+
+This policy exists due to
+
+- ethical concerns about the data gathering for training these models
+- the disproportionate use of electricity and water of building / running them
+- the potential negative influence of LLM-generated content on quality
+- potential copyright violations
+
+This ban of LLM-generated content applies to all parts of the projects,
+including, but not limited to, code, documentation, issues, and artworks.
+An exception applies for purely translating texts for issues and comments to
+English. We may make more exceptions for other accessibility-related uses.
+
+## Project-related use of LLMs
+
+We heavily discourage the use of LLM chat bots as a replacement for reading
+Ruma's documentation and API reference.
+
+Support requests referencing misleading or false LLM output relating to the
+project may be ignored, since it is a waste of time for us to "debug" where
+things went wrong based on this output before human support was sought.