Heads up on new checkstyle rules in the build

[Josh Elser]

As a part of the recent formatting that Christopher did (thanks again, 
for that), he also added the maven-checksyle-plugin to be sure we don't 
just commit a bunch of stuff that's re-broken.

Be aware that the checkstyle plugin is bound to the verify lifecycle 
phase which means that a `mvn package` won't catch it (just like 
findbugs and rat have been operating). It will be a good thing to get in 
the habit of running something like `mvn verify -DskipITs` to make sure 
we don't break any of these rules.... (like I just did :D)

- Josh