docs: add RELEASE

RELEASE.md

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+# Release
+
+1. Merge all changes and let CI run on `main`. You'll have 3 builds, one for each of Windows, macOS and Linux. The Windows and macOS\* builds need to be signed.
+2. Upload the unsigned Windows and macOS builds to R2. **Do _not_ overwrite the previous release's stable builds!**
+3. On the private codesigning repo, kick off a codesign workflow for Windows and macOS. You'll need to provide the URL to the R2-hosted unsigned build for each platform.
+4. Download the signed builds.
+5. Test the signed builds locally. Make sure you install and launch Invoke.
+6. Upload the signed builds to R2. **This time you _should_ overwrite the previous release's stable builds.**
+7. Upload the builds to a new GH release. Follow the format from prior releases. Don't upload the unsigned builds.
+8. Post on Discord in the `releases` channel, and link to that post in the `new-release-discussion` channel.
+
+\*macOS signing is not possible until Apple finalizes our developer account. Skip signing macOS builds for now.
+
+## Auto-Updating Launcher
+
+Once we have macOS code signing set up, we can work on auto-updating for the launcher.
+
+This will hopefully be simple. The electron community provides a free update service for OSS projects and it appears to be very easy to set up.