docs(guide/$location): describe workaround for collocated apps

When using Angular in the root of a domain with HTML5 URLs
where there are links to external paths within the same directory,
the `otherwise` route handler will catch these external files.
This can be fixed by prefixing '.' onto the links to URLs that should
be handled by angular routing.

Original Issue: #3520
Example of Fix: http://fiddle.jshell.net/fgHf6/3/

Closes #3555