README overhaul

1. Remove any "what this affects" sections, except where particularly warranted.
2. Make sure that for each parameter, where applicable, there is a data type and a default value.
3. Make sure that for each parameter that's applicable, there is a note if the parameter is optional.
4. Make sure the links in the README work and are accurate.
5. Update the link in the Contributing section to point here: https://docs.puppetlabs.com/forge/contributing.html
6. General copyediting.
7. Replace "defined type" with "define"

Adjusts README update per comments

-Removes the Build Status link
-Removes two references to the shell script, which has been removed.

Removes an unnecessary phrase.

The script to install no longer depends on platform.