[documentation] Admin Panel installation + usage (#552)

* admin panel documentation

* wrap link so it's clickable

* format img so it works with mkdocs serve

Co-authored-by: tsmethurst <tobi.smethurst@protonmail.com>

docs/admin/admin_panel.md

@@ -1,5 +1,26 @@
 # Admin Control Panel
 
-TODO!
+[gotosocial-admin](https://github.com/superseriousbusiness/gotosocial-admin) is a simple webclient that uses the [admin api routes](https://docs.gotosocial.org/en/latest/api/swagger/#operations-tag-admin) to manage your instance. It uses the same OAUTH mechanism as normal clients (with scope: admin), and as such can be hosted anywhere, separately from your instance, or run locally. A public installation is available here: [https://gts.superseriousbusiness.org/admin](https://gts.superseriousbusiness.org/admin).
 
-For now see [here](https://github.com/superseriousbusiness/gotosocial-admin).
+## Using the panel
+To use the Admin API your account has to be promoted as such:
+```
+./gotosocial --config-path ./config.yaml admin account promote --username YOUR_USERNAME
+```
+After this, you can enter your instance domain in the login field (auto-filled if you run GoToSocial on the same domain), and login like you would with
+any other client.
+
+<p align="middle">
+	<img src="../../assets/admin-panel.png">Screenshot of the GoToSocial admin panel, showing the fields to change an instance's settings</img>
+</p>
+
+You can change the instance's settings like the title and descriptions, and add/remove/change domain blocks including a bulk import/export.
+
+## Installing the panel
+Build requirements: some version of [Node.js](https://nodejs.org) and yarn.
+```
+git clone https://github.com/superseriousbusiness/gotosocial-admin.git && cd gotosocial-admin
+yarn install
+node index.js
+```
+This will compile a static bundle in `public/`, which can be copied to any webhost, or put into your GoToSocial installation in the `web/admin` directory.