doc: Document commit message format

docs/COMMITS.md

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+## About commit messages
+
+Commit messages should follow the [conventional commit specification](https://www.conventionalcommits.org/en/v1.0.0/)
+ 
+The format is: 
+```
+<type>[(optional scope)]: <description>
+
+[optional body]
+
+[optional footer(s)]
+```
+
+The type is one of:
+- **fix**: Commit fixes a bug
+- **feat**: Commit introduces a new feature
+- **refactor**: Commit refactors code
+- **perf**: Commit optimizes performance
+- **doc**: Commit changes or adds documentation
+
+A scope may be appended to the type, for example:
+`feat(renderer): Implement the good lights`
+
+If a commit introduces a breaking API change, a exclamation point (!) is added after the type:
+`feat(renderer)!: New render view api`
+
+Optionally, a breaking change may contain a "BREAKING CHANGE: <description>" footer,
+that explains the change.
+