added contributing file

CONTRIBUTING.md

@@ -0,0 +1,35 @@
+# Contributing
+
+...is welcome!
+
+## Issue tracking / Repository
+
+From issues to wikis: everything is on [GitHub](https://github.com/krawieck/lemmur)
+
+## Architecture
+
+Lemmur is written in Dart using [Flutter](https://flutter.dev/docs). To communicate with Lemmy instances [lemmy_api_client](https://github.com/krawieck/lemmy_api_client) is used.
+
+### State management
+
+[MobX](https://github.com/mobxjs/mobx.dart) is used for global state management, [flutter_hooks](https://github.com/rrousselGit/flutter_hooks) is used for local (widget-level) state management. `StatefulWidget`s are avoided all together and any state logic reuse is moved to a [custom hook](./lib/hooks).
+
+### Project structure
+
+(relative to `lib/`)
+
+- `hooks/`: reusable state hooks
+- `pages/`: fullscreen pages that you navigate to
+- `stores/`: MobX global stores
+- `util/`: utils
+- `widgets/`: reusable widgets; building blocks for pages
+- `main.dart`: entrypoint of the app. Sets up the stores, initializes the themes, renders the first page
+
+### Things to keep in mind
+
+- Be aware that Lemmur supports arbitrary Lemmy instances, don't hardcode instance urls
+- Remember that a user is not obligated to be logged in, contributed widgets should handle this case
+
+## Linting / Formatting
+
+Everything is formatted with `dartfmt` (no flags) and linted with `dartanalyzer` ([see rules](analysis_options.yaml)). Both are enforced by the CI.