Add Fabric setup instructions

docs/mscs/adjusting-world-server-properties/fabric.md

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+---
+layout: default
+title: Fabric
+nav_order: 7
+parent: Adjusting World & Server Properties
+permalink: /docs/mscs/adjusting-world-server-properties/fabric
+---
+
+# Fabric
+
+This guide describes how to configure MSCS to run a world using [Fabric][fabric].
+
+There are several ways to install Fabric.
+This document describes the current recommended method,
+which uses an executable [server launcher][launcher] instead of a separate installer.
+Manual installation using an [installer JAR][installer] is not covered.
+
+## Initial configuration
+
+1. [Download the server launcher][launcher] into the Minecraft Server Control Script's server directory.
+
+   Note: the URL in the following example will not work.
+   You must use the `curl` command provided on the download page.
+   ```
+   cd /opt/mscs/server
+   curl -OJ https://meta.fabricmc.net/v2/versions/loader/GameVersion/LoaderVersion/InstallerVersion/server/jar
+   ```
+2. When the download completes, it will tell you the filename that was saved.
+   Take note of it (or copy it to your clipboard) for use in a future step.
+
+   Continuing the artificial (non-functional) example from the previous step...
+   ```
+   $ curl -OJ https://meta.fabricmc.net/v2/versions/loader/GameVersion/LoaderVersion/InstallerVersion/server/jar
+     % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
+                                    Dload  Upload   Total   Spent    Left  Speed
+   100  143k    0  143k    0     0   109k      0 --:--:--  0:00:01 --:--:--  109k
+   curl: Saved to filename 'fabric-server-mc.GameVersion-loader.LoaderVersion-launcher.LauncherVersion.jar'
+   ```
+3. Create a world.
+   (Replace "fabric-example" with your desired world name here and in future steps.)
+   ```
+   mscs create fabric-example
+   ```
+4. Configure the world to use the Fabric JAR by configuring some settings in `mscs.properties`.
+
+   Note: this uses the filename from the artificial example above.
+   When you run the first command, you must use the filename that you observed in step 2 instead of this example's artificial filename.
+   ```
+   echo 'mscs-server-jar=fabric-server-mc.GameVersion-loader.LoaderVersion-launcher.LauncherVersion.jar' >> /opt/mscs/worlds/fabric-example/mscs.properties
+   echo 'mscs-server-url=' >> /opt/mscs/worlds/fabric-example/mscs.properties
+   ```
+5. Accept the EULA.
+   ```
+   echo 'eula=true' > /opt/mscs/worlds/fabric-example/eula.txt
+   ```
+6. (optional) Customize your world's settings in `mscs.properties` and `server.properties`.
+   See [Adjusting World & Server Properties](/docs/mscs/adjusting-world-server-properties) to learn about MSCS-specific settings.
+   The Minecraft Wiki documents [the settings that are configurable in `server.properties`][server.properties].
+7. Start the server.
+   ```
+   mscs start fabric-example
+   ```
+
+## Updating
+To update, repeat steps 1 and 2 above.
+Then, change `mscs-server-jar` in your world's `mscs.properties` to the updated version's filename.
+Finally, restart your world.
+
+[fabric]: https://fabricmc.net
+[launcher]: https://fabricmc.net/use/server/
+[installer]: https://fabricmc.net/wiki/player:tutorials:install_server
+[server.properties]: https://minecraft.fandom.com/wiki/Server.properties