docs: add instructions for releasing, so that I don't forget a step.

README.md

@@ -127,3 +127,17 @@ to Jellyfin:
 Go to `Dashboard>Catalog>(Gear)>(Plus)` and paste the provided link into
 the field labeled `Repository URL`, give the plugin a descriptive name
 too.
+
+## Releasing a new version
+
+1. Write the changelog: `git log --oneline $prev_version..`
+2. Update the following files to include up-to-date version numbers
+   and changelogs, if applicable:
+   - `README.md`
+   - `Jellyfin.Plugin.SmartPlaylist/build.yaml`
+   - `Jellyfin.Plugin.SmartPlaylist/jellyfin-smart-playlist.csproj`
+   Don't forget to also bump the ABI version of Jellyfin.
+3. Push the changes
+4. Create a new release with the changelog, mark as pre-release if
+   applicable.
+5. Done! The build pipeline will do the rest.