(maint) Add COMMITTERS.md and CONTRIBUTING.md

In order to make contributions more accessible to the community,
add COMMITTERS.md and CONTRIBUTING.md so that there are instructions
and resources for those who would like to contribute to the strings
module.
(maint) Remove references to stable in COMMITTERS

Since puppet strings is a very small project, at the moment we
don't need to maintain a master and a stable branch. As a result,
the COMMITTERS.md guide should not contain references to the stable
branch or include information around dealing with both the master
and stable branch. Remove these references so that COMMITTERS is
consistent with our approach to the strings repository.
(PDOC-10) Update README.md to be more detailed

Since puppet strings will soon release a 0.1.0 version, update the
README.md file to include the necessary details about the project.
(maint) Add LICENSE file

Add an Apache License for this project to be consistent with other
puppetlabs modules.
(PDOC-10) Try to simplify the installation

The instructions for installation provided a lot of different
alternatives. In order to quickly answer the question of "how do I use
this" we can just give the most common ways of getting it installed.
Merge branch 'hkenney-maint/master/pdoc-10_update_readme_md'

* hkenney-maint/master/pdoc-10_update_readme_md:
  (PDOC-10) Try to simplify the installation
  (maint) Add LICENSE file
  (PDOC-10) Update README.md to be more detailed
(maint) Remove reference to other platforms

The "other platforms" is language from puppet where we don't always have
access to various OS and version combinations. Strings is much simpler
and so it isn't really relevant.
Merge branch 'hkenney-maint/master/add_committers_and_contributing_md'

* hkenney-maint/master/add_committers_and_contributing_md:
  (maint) Remove reference to other platforms
  (maint) Remove references to stable in COMMITTERS
  (maint) Add COMMITTERS.md and CONTRIBUTING.md

Closes GH-11