Updates to the google-java-format IntelliJ plugin.

* Add some more docs (both user-level and developer) to the README.md.
* Mark the plugin as available in all JetBrains IDEs.
* Mark it as unsupported in 2016.3. Which it is. (For now.)

MOE_MIGRATED_REVID=142272002
diff --git a/idea_plugin/google-java-format.iml b/idea_plugin/google-java-format.iml
index 2808d73..a5cd516 100644
--- a/idea_plugin/google-java-format.iml
+++ b/idea_plugin/google-java-format.iml
@@ -10,6 +10,5 @@
     </content>
     <orderEntry type="inheritedJdk" />
     <orderEntry type="sourceFolder" forTests="false" />
-    <orderEntry type="library" name="google-java-format-1.1-20160728.050102-25-all-deps" level="project" />
   </component>
-</module>
\ No newline at end of file
+</module>