Allow JRuby builds to fail

JRuby is having problems with the NTLMHash hash calculations and
validations and we don't have time to fix them now.  Additionally,
metasploit-credential only support JRuby because metasploit_data_models
did from a community RFE, so JRuby support isn't critical to
metasploit-credential release.
Include branch for travis-ci badge

[ci skip]

This way build failures on branches won't influence badge.
Expand Documentation in README

[ci skip]

Cover how to setup database, generate, and read.
Fix headers in README

[ci skip]
Include Testing in README

Since the Documentation section required documenting how to setup the
database.yml, it made sense to also include a Testing section that
included the same information and how to run the specs.
Merge branch 'master' into bug/MSP-10963/realm-uniqueness

MSP-10963