Support 'createhome' parameter in salt.modules.pw_user.add on FreeBSD
Merge pull request #6762 from billfehring/freebsd-pw_user-createhome

Support 'createhome' parameter in salt.modules.pw_user.add on FreeBSD
Expanded on Formulas Salt version requirements
Improved Formula installation instructions

Refs #6739
Fleshed out the "Writing Formula" section
On bootstrap failure, also cleanup.