[Java] Update README with instructions for IntelliJ users

[asfimport]

IntelliJ needs to be configured to use the errorprone compiler and this is not currently documented, making it hard for new contributors to build/test the project. We can pretty much just link to the instructions at https://errorprone.info/docs/installation

Reporter: Andy Grove / @andygrove

_{Note: This issue was originally created as ARROW-7763. Please see the migration documentation for further details.}

[lidavidm]

There are error-prone instructions (albeit very terse ones) in the docs now showing how to disable them in IntelliJ. https://arrow.apache.org/java/current/developers/building.html#intellij