Updates Readme with attribute info
Updates Readme with attribute info

Adds documentation about what attributes are available to tweak as well
as additional info about update the JVMVersion by default and how to
disable it if you don't want it.

Signed-off-by: Kihyeon Kim <3900da17246426210a3d6fd6e4d6195079876ae8@gmail.com>

pivotal-sprout/sprout-jetbrains-editors,wendorf/sprout-jetbrains-editors