Add conventions

Author: steffenkleinle

README.md

@@ -14,3 +14,31 @@ A few resources to get you started if this is your first Flutter project:
 For help getting started with Flutter development, view the
 [online documentation](https://docs.flutter.dev/), which offers tutorials,
 samples, guidance on mobile development, and a full API reference.
+
+## Conventions
+
+### Code Style
+
+We follow the [Effective Dart code style](https://dart.dev/effective-dart/style).
+
+Code should be formatted using `dart format` ([docs](https://dart.dev/tools/dart-format)).
+
+### Commits, Branches and Pull Requests
+
+Branch names should be written using kebab-case and have the following schema:
+
+```
+<issue_key>-your-branch-name
+
+1234-commit-message-documentation
+```
+
+Commit messages and PR names should have the following schema:
+```
+<issue_key>: Your commit message
+
+1234: Add commit message documentation
+```
+
+See [this guide](https://github.com/erlang/otp/wiki/Writing-good-commit-messages) for a general reference on how to
+write good commit messages.