docs: add README, CONTRIBUTING, LICENCE, and .gitignore

- Add README with repository overview and usage instructions
- Add CONTRIBUTING with branch naming, commit, and PR guidelines
- Add MIT LICENCE
- Add .gitignore for Windows, macOS, Linux, IDE, and Claude Code files

CONTRIBUTING.md

@@ -0,0 +1,45 @@
+# Contributing
+
+Thanks for considering contributing to docker-infra.
+
+## Getting started
+
+1. Fork the repository on Gitea.
+2. Clone your fork locally.
+3. Create a branch for your changes.
+
+## Branch naming
+
+Use the format `<type>/<short-description>`:
+
+| Type     | Usage                             |
+| -------- | --------------------------------- |
+| feature  | New functionality                 |
+| fix      | Bug fix                           |
+| docs     | Documentation changes             |
+| chore    | Tooling, dependencies, maintenance |
+
+Examples: `feature/add-postgres-compose`, `docs/update-readme`.
+
+## Commit messages
+
+Follow the [Conventional Commits](https://www.conventionalcommits.org/) format:
+
+```
+<type>(<scope>): <description>
+```
+
+Keep the subject line under 50 characters. Use the imperative mood
+("add feature", not "added feature").
+
+## Pull requests
+
+- Keep changes focused — one concern per pull request.
+- Update or add documentation if your change affects usage.
+- Ensure your branch is up to date with `main` before opening a PR.
+
+## Code style
+
+- Use British English spelling in all documentation and comments.
+- Follow the existing style of the files you are editing.
+- End YAML files with a trailing newline.