Pointing to the Belle docs for building from source
Oops updated wrong branch
Fix order of null-check versus dotting through to .UmbracoContext.

The order of operations in the constructor dots through to the _routingContext.UmbracoContext before checking if the value was null and throwing the argument exception (which really isn't an ArgumentException...)
Merge pull request #141 from IDisposable/patch-1

Fix order of null-check versus dotting through to .UmbracoContext.