Add note on compiler errors in readme

Unsafe is funny

Author: Col-E

README.md

@@ -50,4 +50,11 @@ implementation group: 'software.coley', name: 'lljzip', version: zipVersion
 implementation "software.coley:lljzip:${zipVersion}"
 ```
 
-For example usage see the [tests](src/test/java/software/coley/lljzip).
+For example usage see the [tests](src/test/java/software/coley/lljzip).
+
+## Building
+
+Due to some `sun.misc.Unsafe` hacks _(For performance and long addressing)_, you will get compiler warnings when first opening the project in IntelliJ.
+You can resolve this by changing the compiler target:
+
+![intellij compiler settings](docs/compiler-settings.png)