add velocity integration documentation (fix Minestom#8)

setup/velocity-integration.md

@@ -0,0 +1,111 @@
+---
+description: Step by step guide on how to set up velocity for Minestom
+---
+
+# Velocity Integration
+
+Using Velocity in your Minestom project is very simple, you only need to follow 3 simple steps.
+
+* Install Velocity
+* Set up Velocity
+* Enable Velocity in your Minestom server
+
+## Installing Velocity
+You can download velocity from [the official website](https://papermc.io/downloads/velocity). You need to start it and let it create all necessary files. This shouldn't take too long, and it's recommended to use a starter script.
+
+{% tabs %}
+{% tab title="Bash (macOS and Linux)" %}
+For Linux create a `starter.sh` file and for macOS create a `starter.command` file. Make sure you put them into the same folder as your Velocity jar. Replace `<your file without path>` with the name of your Velocity jar file.
+
+```bash
+#! /bin/bash --
+
+TIME=30
+DIR="$(dirname "$0")"
+SERVER=$(basename $DIR)
+FILENAME="<your file without path>.jar"
+
+echo "$SERVER: starting..."
+cd $DIR
+while :
+do
+	# More memory: change -Xms and -Xmx. Do not change other options.
+	java -Xms512M -Xmx512M -XX:+UseG1GC -XX:G1HeapRegionSize=4M -XX:+UnlockExperimentalVMOptions -XX:+ParallelRefProcEnabled -XX:+AlwaysPreTouch -jar $FILENAME
+	echo "$SERVER: Java stopped or crashed. Waiting $TIME seconds..."
+	sleep $TIME
+done
+```
+{% endtab %}
+{% tab title="Batch (Windows)" %}
+{% hint style="warning" %}
+This has not been tested yet. If you own a Windows computer, try it and check if it works.
+{% endhint %}
+
+Create a `starter.bat` file in the same folder as your Velocity server jar. Replace `<your file without path>` with the name of your Velocity server jar file.
+
+```batch
+@echo off
+
+set time=30
+set dir=%~dp0
+set filename="<your file without path>.jar"
+
+echo "%dir%: starting..."
+cd %dir%
+:loop
+:: More memory: change -Xms and -Xmx. Do not change other options.
+java -Xms512M -Xmx512M -XX:+UseG1GC -XX:G1HeapRegionSize=4M -XX:+UnlockExperimentalVMOptions -XX:+ParallelRefProcEnabled -XX:+AlwaysPreTouch -jar %filename%
+echo "%dir%: Java stopped or crashed."
+timeout %time% > NUL
+goto loop
+```
+{% endtab %}
+{% endtabs %}
+
+After you have started Velocity you should see a few new files and folders appearing such as `velocity.toml` and `forwarding.secret`.
+
+## Setting up Velocity
+The default settings in `velocity.toml` should be fine, but there are some things we need to change. In the `[servers]` category you'll see some pre-defined servers, which you most likely need to change or remove. In this example we will remove all servers except for `lobby`. Change `lobby`'s port to the port you defined when binding your Minestom server. Here's an example:
+
+```toml
+[servers]
+# Configure your servers here. Each key represents the server's name, and the value
+# represents the IP address of the server to connect to.
+lobby = "127.0.0.1:25565"
+
+# In what order we should try servers when a player logs in or is kicked from a server.
+try = [
+    "lobby"
+]
+
+[forced-hosts]
+# Configure your forced hosts here.
+"example.com" = [
+    "lobby"
+]
+```
+
+Make sure to change `player-info-forwarding-mode` to `MODERN`. You can now save the `velocity.toml` file and move onto the `forwarding.secret` file. This is a text file, so you can open it using your preferred text editor. We highly recommend changing the secret instead of using the default. You will need this secret later, so don't forget it. **Do not give out your secret to anybody!** The secret is used to ensure that player info forwarded by Velocity comes from your proxy and not from someone pretending to run Velocity. [More information](https://docs.papermc.io/velocity/configuration)
+
+## Setting up the Minestom server
+In your main file, just before binding the server, use the `VelocityProxy.enable()` method. If you use `MojangAuth` you will need to remove that, but not to worry: your server will not be in offline mode. The proxy makes sure all connections are secure.
+
+```java
+// Don't use: MojangAuth.init();
+VelocityProxy.enable("very secret secret");
+minecraftServer.start("0.0.0.0", 25565);
+```
+
+You're done! You can now start the proxy and the Minestom server.
+
+## Troubleshooting
+* Connection lost: "Invalid proxy response!"\
+You entered the wrong port, IP address or didn't start the proxy. You can find the port of the proxy in the `velocity.toml` under `bind`
+
+* Connection lost: "Unable to connect you to (server). Invalid proxy response!"\
+Make sure you changed `player-info-forwarding-mode` to `MODERN`
+
+* Connection lost: "Unable to connect you to (server). Please try again later."\
+You didn't set up the proxy correctly (in `velocity.toml`) file. Make sure it has the correct port and IP address, the Minestom server is running, and you are using the correct secret.
+
+If you still have issues you can join the [Discord server](https://discord.gg/Pt9Mgd9cgR)