Add note about JDK_16 in readme

Author: qwwdfsad

README.md

@@ -161,7 +161,7 @@ to Gradle (in Preferences -> Build, Execution, Deployment -> Build Tools -> Grad
 ### Requirements
 
 * JDK >= 1.8 referred to by the `JAVA_HOME` environment variable.
-* JDK 1.6 referred to by the `JDK_16` environment variable.
+* JDK 1.6 referred to by the `JDK_16` environment variable. It is okay to have `JDK_16` pointing to `JAVA_HOME` for external contributions.
 
 ## Contributions and releases