Add an updating guide

docs/setup/server/updating.md

@@ -0,0 +1,21 @@
+If you had followed the [setup guide](index.md), you'll have installed Fosscord using [Git](https://git-scm.com/).
+Thus, you can update the server by running `git pull`.  
+
+If you had made any changes locally, you may run into merge conflicts,
+where the Fosscord team has made changes to the same code you changed. If it's not important to you, you can simply run `git reset --hard HEAD`
+*which will delete all your changes*. If you want to keep them, you'll have to go through each conflict and resolve them.  
+
+After downloading the new version, go through the setup guide as normal again:
+
+!!! error "Do not run `npm run sync:db` with existing databases! You may suffer dataloss!"
+
+```bash
+# Install any new javascript packages
+npm i
+
+# Build and generate schema
+npm run setup
+
+# Start the server
+npm run start
+```