Document Git access and fork-and-PR contribution model

infrastructure.md

@@ -72,6 +72,32 @@ Plus the `co-op` organization:
 - [**co-op/docs**](https://git.inference.coop/co-op/docs) — this documentation.
 - [**co-op/design-assets**](https://git.inference.coop/co-op/design-assets) — logos, fonts, brand materials.
 
+## Contributing (the Git is yours, too)
+
+Everything the co-op runs is open source and lives at
+[git.inference.coop](https://git.inference.coop) — the website, this
+documentation, the member portal, the dashboard, the admin panel, and the
+gateway. As a member, you can browse all of it and propose changes.
+
+**Who can sign in.** Git access is tied to your membership: you log into the Git
+with the same single sign-on you use for the chat. Members are in automatically
+(through the `members` group); when a membership lapses, Git access lapses with it.
+
+**How to contribute.** Anyone can read the repos without an account. To make a
+change, fork the repo, edit in your fork, and open a **pull request**:
+
+1. Log into [git.inference.coop](https://git.inference.coop) with your co-op account.
+2. **Fork** the repo you want to change (e.g. `co-op/docs`).
+3. Make your edits in your fork and commit them.
+4. Open a **pull request** back to the original repo, describing your change.
+
+**All changes are reviewed.** Nothing merges directly into `main` — every change
+comes in as a pull request that an admin reviews and approves first. You don't
+need to be able to create repos or organizations to contribute; you just fork,
+edit, and ask for review.
+
+Questions about the Git itself? Write to info@inference.coop.
+
 ## Models and privacy
 
 Inference runs through [Tinfoil](https://tinfoil.sh/inference), which provides