(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