Add CONTRIBUTING.md

.github/CONTRIBUTING.md

@@ -0,0 +1,33 @@
+# Contributing
+
+Thank you for considering contributing to the `phptg/bot-api` library!
+
+## Reporting issues
+
+Bug reports and feature requests are welcome via [GitHub Issues](https://github.com/phptg/bot-api/issues).
+Please include the library version, the PHP version, and a minimal snippet that reproduces the problem.
+For questions and discussion, use the author's [Telegram chat](https://t.me/predvoditelev_chat).
+
+## Development setup
+
+Requirements: 64-bit PHP 8.2–8.5 and [Composer](https://getcomposer.org/download/).
+
+Fork the repository, clone it and run `composer install`.
+
+See [Internals](../docs/internals.md) for running tests, static analysis, code style and the other tools.
+
+## Rules
+
+- The library has **zero runtime dependencies** — nothing may be added to the `require` section of
+  `composer.json`.
+- Backward compatibility is preserved as much as possible. A new method parameter is always added **last**,
+  with a default value, regardless of its position in the Telegram Bot API documentation.
+- Tests live under `tests/`, mirroring the structure of `src/`.
+- Every user-visible change needs a `CHANGELOG.md` entry under the topmost `under development` heading, in the
+  form `- New #123: Add SendMessage method.`, where `#123` is the pull request number. Use `New` for new features,
+  `Enh` for improvements, `Chg` for changes affecting existing usage, `Bug` for fixes.
+- Update the documentation (`README.md`, `docs/`) when behavior or the public API changes.
+
+## Pull requests
+
+Keep pull requests focused on a single change and make sure all CI checks pass.

docs/internals.md

@@ -49,18 +49,26 @@ The code is statically analyzed with [Psalm](https://psalm.dev/). To run static
 
 ## Code style
 
-Package used [PHP CS Fixer](https://cs.symfony.com/) to maintain [PER CS 2.0](https://www.php-fig.org/per/coding-style/)
+Package used [PHP CS Fixer](https://cs.symfony.com/) to maintain [PER CS 3.0](https://www.php-fig.org/per/coding-style/)
 code style. To check and fix code style:
 
 ```shell
 composer cs-fix
 ```
 
+## Refactoring
+
+The code is refactored with [Rector](https://getrector.com/). To apply it:
+
+```shell
+composer rector
+```
+
 ## Dependencies
 
-Use [ComposerRequireChecker](https://github.com/maglnet/ComposerRequireChecker) to detect transitive
-[Composer](https://getcomposer.org) dependencies:
+Use [Composer Dependency Analyser](https://github.com/shipmonk-rnd/composer-dependency-analyser) to detect unused,
+shadow and misplaced [Composer](https://getcomposer.org) dependencies:
 
 ```shell
-./vendor/bin/composer-require-checker
+composer dependency-analyser
 ```