Update java.md for clarity
Update java.md for clarity

Changed Java download link to point to the JDK not JRE download links.
Added instructions for JAVA_HOME for MacOS
Added section to pull a sample test project between java/maven setup and running your first test.
DylanLacey/docs,whoward/docs,rossrowe/docs,tonytamsf/docs,ndmanvar/docs,AbhijitPendyal/docs,cvan/docs