(doc) Update COMMITTERS and CONTRIBUTING

Without this patch the documentation describing our workflow and process
is out of date for Facter.  This is a problem because community
contributors and people new to Puppet Labs have a more difficult time
learning how to submit contributions and merge contributions into the
codebase.

This patch addresses the problem by copying the COMMITTERS and
CONTRIBUTING documents from Puppet and customizing them specifically to
Facter.

[ci skip]
Merge pull request #395 from jeffmccune/update_contributing_doc

(doc) Update COMMITTERS and CONTRIBUTING