Create GOVERNANCE.md

see #81 for context

GOVERNANCE.md

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+The Wikimate project strives for a transparent and welcoming maintenance process.
+Below are some guidelines for current and prospective maintainers.
+Anyone is welcome to propose changes to this document via issues or pull requests.
+
+Regular contributors are to be given collaborator status
+(which includes commit access, the ability to merge PRs, make releases, etc.).
+Note that at the moment this can only be done by the repository owner, @hamstar.
+Contributors are encouraged to ask for collaborator access once you have had a few accepted PRs, and would like to help maintaining the repository.
+
+## Guidelines for commits and pull requests
+
+1. **Every change** (except for very minor ones such as spelling fixes) **should be made via pull requests**,
+   rather than as direct commits to the repository.
+2. **Maintainers should not merge their own pull requests**.
+   This allows every change to be validated by at least another maintainer
+3. Pull requests should comprise a single feature or bugfix.
+   **Unrelated changes should be sent as separate PRs.**
+   The exception are minor code cleanup changes,
+   which can be included (as a separate commit) in the PR that prompted them.
+4. **Commits should be atomic** (as small as possible while still representing a self-consistent set of changes)
+   and have descriptive commit messages.
+5. **Every PR should include a CHANGELOG.md entry**.
+   This makes it much easier to prepare releases,
+   and allows the change author to properly summarize it.
+
+## Process for releasing a new version of Wikimate
+
+[TODO]