Refresh the supporting documentation

Separate the README into sections for easier navigation
Add CONTRIBUTING guidelines, copied from the Hydra template
Add the Apache 2.0 license to make it clear this is open-source software
Allow pidfile value to be changed
Merge pull request #8 from mjgiarlo/documentation_refresh

Refresh the supporting documentation
Merge pull request #9 from mjgiarlo/respect_pidfile_option

Allow pidfile value to be changed
Updated README