admin: move Gitea migration to its own page

It doesn't feel right to have such guide on the installation page, it
feels more natural to have it's own page. This also keeps the
'installation' page clean, which currently feels more like an index
page, given it's linking to two other pages (installation from {binary,docker}).

docs/admin/gitea-migration.md

@@ -0,0 +1,65 @@
+---
+title: 'Gitea migration'
+license: 'CC-BY-SA-4.0'
+---
+
+This guide describes how to go from Gitea to Forgejo if Gitea is installed via a package manager.
+
+## Arch Linux
+
+Arch Linux provides package for both Gitea and Forgejo,
+but they install to different locations and run as different users.
+Therefore, a small amount of work is needed to transition from one to the other.
+
+First step is to install the Forgejo package, and stop the Gitea service.
+
+    $ pacman -S forgejo
+    $ systemctl stop gitea
+
+### Configuration migration
+
+Now, we can copy the Gitea configuration over the default Forgejo one.
+We need to set the group owner and group write permission so Forgejo can write to it.
+
+    $ cp /etc/gitea/app.ini /etc/forgejo/app.ini
+    $ chown root:forgejo /etc/forgejo/app.ini
+    $ chmod g+w /etc/forgejo/app.ini
+
+### Data migration
+
+If we want to leave a copy of the Gitea data untouched (recommend in case of mistakes)
+the next step is to copy the existing data to the Forgejo user's home directory.
+We need to change the ownership of the files to the `forgejo` user and group too.
+
+    $ cp -r /var/lib/gitea/* /var/lib/forgejo
+    $ chown -R forgejo: /var/lib/forgejo/*
+
+Finally, we need to update the configuration, which currently points to `/var/lib/gitea`,
+to point to the new location.
+Edit `/etc/forgejo/app.ini` and replace all instances of `/var/lib/gitea` with `/var/lib/forgejo`.
+
+### Data migration (no copy)
+
+If you're not concerned about being able to roll back to your Gitea installation,
+you can simply change the owner of the files in `/var/lib/gitea`.
+There's then no need to change the configuration.
+
+    $ chown -R forgejo: /var/lib/gitea/*
+
+### Starting Forgejo
+
+Whichever data migration you've chosen, it's now time to start the Forgejo service.
+
+    $ systemctl start forgejo
+
+Check to see that the service has started with no issues.
+
+    $ systemctl status forgejo
+
+...and set the service to start automatically.
+
+    $ sytemctl enable forgejo
+
+Finally, if you're happy with everything, you can uninstall Gitea.
+
+    $ pacman -R gitea

docs/admin/installation.md

@@ -13,70 +13,13 @@ steps:
 - Connect to the web interface and complete the configuration
 - And finally register the first user which will be granted administrative permissions
 
+If you already have Gitea installed through your package manager, look at the [Gitea
+migration](../gitea-migration/) guide for information on how to install Forgejo, while
+preserving your data from your Gitea installation.
+
 Forgejo is also available for installation using package managers on many platforms. At this
 time, Forgejo has been successfully adapted for use on various platforms, including Alpine Linux, Arch
 Linux, Debian, Fedora, Gentoo, Manjaro, and the Nix ecosystem. These
 platform-specific packages are under the care of distribution packagers, and specific packages are
 currently undergoing testing. For a curated inventory, please refer to
 [the "Delightful Forgejo" list](https://codeberg.org/forgejo-contrib/delightful-forgejo#packaging).
-
-# Migration from Gitea
-
-## Arch Linux
-
-Arch Linux provides package for both Gitea and Forgejo,
-but they install to different locations and run as different users.
-Therefore, a small amount of work is needed to transition from one to the other.
-
-First step is to install the Forgejo package, and stop the Gitea service.
-
-    $ pacman -S forgejo
-    $ systemctl stop gitea
-
-### Configuration migration
-
-Now, we can copy the Gitea configuration over the default Forgejo one.
-We need to set the group owner and group write permission so Forgejo can write to it.
-
-    $ cp /etc/gitea/app.ini /etc/forgejo/app.ini
-    $ chown root:forgejo /etc/forgejo/app.ini
-    $ chmod g+w /etc/forgejo/app.ini
-
-### Data migration
-
-If we want to leave a copy of the Gitea data untouched (recommend in case of mistakes)
-the next step is to copy the existing data to the Forgejo user's home directory.
-We need to change the ownership of the files to the `forgejo` user and group too.
-
-    $ cp -r /var/lib/gitea/* /var/lib/forgejo
-    $ chown -R forgejo: /var/lib/forgejo/*
-
-Finally, we need to update the configuration, which currently points to `/var/lib/gitea`,
-to point to the new location.
-Edit `/etc/forgejo/app.ini` and replace all instances of `/var/lib/gitea` with `/var/lib/forgejo`.
-
-### Data migration (no copy)
-
-If you're not concerned about being able to roll back to your Gitea installation,
-you can simply change the owner of the files in `/var/lib/gitea`.
-There's then no need to change the configuration.
-
-    $ chown -R forgejo: /var/lib/gitea/*
-
-### Starting Forgejo
-
-Whichever data migration you've chosen, it's now time to start the Forgejo service.
-
-    $ systemctl start forgejo
-
-Check to see that the service has started with no issues.
-
-    $ systemctl status forgejo
-
-...and set the service to start automatically.
-
-    $ sytemctl enable forgejo
-
-Finally, if you're happy with everything, you can uninstall Gitea.
-
-    $ pacman -R gitea