Some punctuation fixes, XML Configuration examples were misinterpreted using indentation only, expanded on ZK paths.

Biggest non-grammatical change is adding in a reference to
the $hadoop.registry.zk.root when listing children paths such
as /services and /users. IMO, more clear that everything is beneath
that root path in ZK.
Merge pull request #4 from joshelser/YARN-913/YARN-2683-registry-config-docs

Some punctuation fixes, XML Configuration examples were misinterpreted u...