cover null case for belongsTo relationship
fix typo - missing close array
Remove inaccurate information from README.

This truncates the README considerably, but considering the previous
version was months out of date, it wasn't being helpful to newcomers.

A reference to the guide and its correctness at version 11 is added.
Merge pull request #575 from shwoodard/breaking-changes-typo

fixing documentation typo - missing close array
Merge pull request #597 from trek/shorten-readme

Remove inaccurate information from README.
Merge pull request #564 from jefflab/null-belongsTo

cover null case for belongsTo relationship
Formatting