docs: Add note about JBR

CONTRIBUTING.md

@@ -29,6 +29,18 @@ to create a [fork](https://github.com/nea89o/Firmament/fork). This is your own c
 You can load that fork using IntelliJs "New" -> "Project from version control" import option. You might need to
 authenticate your GitHub account to IntelliJ during this process or at a later point in time.
 
+### JBR
+
+By default, Firmament tries to launch with hotswapping enabled in the devenv. This will fail if your JVM does not 
+support hotswapping. In that case you can either remove the hotswapping arguments, or you can use [JBR](jbr). You can
+manually select JBR in your run configuration, after it has been generated by gradle.
+
+```
+-XX:+AllowEnhancedClassRedefinition -XX:HotswapAgent=external -javaagent:SOMEPATH
+```
+
+### Features
+
 Typically, for each new set of features you will create a branch and then create a pull request back to the main
 Firmament repo. Note that Firmament makes use of commit names to generate a changelog. As such the first line of each
 commit should be something that can be interpreted by an end user. If you want to make an internal change you can use
@@ -37,3 +49,4 @@ each feature. Don't worry if you have any problems with your git history, your p
 rewritten to be fixed (but it would help me if you can keep your commit history clean).
 
 [discord]: https://discord.gg/64pFP94AWA
+[jbr]: https://github.com/JetBrains/JetBrainsRuntime/releases/tag/jbr-release-21.0.5b631.16