nixos/forgejo: changelog and migration instructions

nixos/doc/manual/release-notes/rl-2311.section.md

@@ -139,6 +139,8 @@
 
 - [c2FmZQ](https://github.com/c2FmZQ/c2FmZQ/), an application that can securely encrypt, store, and share files, including but not limited to pictures and videos. Available as [services.c2fmzq-server](#opt-services.c2fmzq-server.enable).
 
+- [forgejo](https://forgejo.org/), a git forge. Previously deployed as a drop-in to gitea. Available as [services.forgejo](#opt-services.forgejo.enable). See migration instructions in [manual](https://nixos.org/manual/nixos/stable#module-forgejo)
+
 ## Backward Incompatibilities {#sec-release-23.11-incompatibilities}
 
 - `network-online.target` has been fixed to no longer time out for systems with `networking.useDHCP = true` and `networking.useNetworkd = true`.

nixos/modules/services/misc/forgejo.md

@@ -0,0 +1,25 @@
+# Forgejo {#module-forgejo}
+
+Forgejo is a soft-fork of gitea, with strong community focus, as well
+as on self-hosting and federation. [Codeberg](https://codeberg.org) is
+deployed from it.
+
+See [upstream docs](https://forgejo.org/docs/latest/)
+
+## Migration from Gitea {#module-forgejo-migration-gitea}
+
+The method of choice for running forgejo used to be with the
+`services.gitea` module. For migrating such a setup to the
+`services.forgejo` module (for default options):
+
+```sh
+systemctl stop gitea
+mv /var/lib/gitea /var/lib/forgejo
+runuser -u postgres -- psql -c '
+  ALTER USER gitea RENAME TO forgejo;
+  ALTER DATABASE gitea RENAME TO forgejo;
+'
+nixos-rebuild switch
+chown -R forgejo:forgejo /var/lib/forgejo
+systemctl restart forgejo
+```

nixos/modules/services/misc/forgejo.nix

@@ -677,5 +677,6 @@ in
     };
   };
 
+  meta.doc = ./forgejo.md;
   meta.maintainers = with lib.maintainers; [ bendlas emilylange ];
 }