docs: add release instructions (#272)

Author: aslilac

CONTRIBUTING.md

@@ -144,5 +144,8 @@ To maintain code quality, ensure you run the following before submitting any cha
 
 4. Open a pull request to the main repository.
 
+Maintainers can find release and signing instructions in
+[RELEASING.md](RELEASING.md).
+
 Thank you for contributing! If you have any questions or need further assistance,
 feel free to open an issue.

RELEASING.md

@@ -0,0 +1,59 @@
+# Releasing Coder Desktop
+
+These tasks require access to Coder's Apple Developer team and admin access to
+this repository.
+
+## Releasing a new version
+
+Versions come from Git tags of the form `vX.Y.Z` (see `scripts/version.sh`).
+Pushing a tag doesn't start a workflow, but the GitHub release needs a tag to
+point at.
+
+1. Tag the commit on `main` that you want to release, and push the tag:
+
+   ```bash
+   git tag vX.Y.Z
+   git push origin vX.Y.Z
+   ```
+
+2. Wait for the `release` workflow run for that commit on `main` to finish.
+   It publishes the `preview` build and updates the appcast, so publishing the
+   release while it is still running can race on the appcast update.
+3. [Create a GitHub release](https://github.com/coder/coder-desktop-macos/releases/new)
+   from the tag and write the release notes. The release notes are used as the
+   update description in the Sparkle appcast, so write them before publishing.
+4. Publishing the release starts the `release` workflow, which builds, signs,
+   and notarizes the app, uploads the assets to the release, updates the
+   appcast, and opens a pull request to update the
+   [homebrew-coder](https://github.com/coder/homebrew-coder) cask. Wait for it
+   to finish, then review and merge the cask pull request.
+
+## Updating provisioning profiles
+
+Release builds are signed with two provisioning profiles, one for the app
+(`com.coder.Coder-Desktop`) and one for the network extension
+(`com.coder.Coder-Desktop.VPN`). CI reads them from these repository secrets:
+
+| Secret                                         | Profile file                               |
+| ---------------------------------------------- | ------------------------------------------ |
+| `CODER_DESKTOP_APP_PROVISIONPROFILE_B64`       | `Coder_Desktop_App.provisionprofile`       |
+| `CODER_DESKTOP_EXTENSION_PROVISIONPROFILE_B64` | `Coder_Desktop_Extension.provisionprofile` |
+
+When a profile expires or needs regenerating:
+
+1. Sign in to the [Apple Developer portal](https://developer.apple.com/account/resources/profiles/list)
+   and open **Certificates, Identifiers & Profiles** > **Profiles**.
+2. Regenerate or edit the profile if needed, then download it.
+3. Base64-encode the downloaded file and copy the output:
+
+   ```bash
+   cat Coder_Desktop_App.provisionprofile | base64
+   cat Coder_Desktop_Extension.provisionprofile | base64
+   ```
+
+4. Paste the output into the matching secret under **Settings** >
+   **Secrets and variables** > **Actions**.
+
+To check new profiles before cutting a release, run the `release` workflow
+manually with **dryrun** enabled. The build is uploaded as a workflow artifact
+instead of a release asset.