Refocusing README.md and CONTRIBUTING.md

Refocusing README.md on implementation and tasks related to
development; Refocusing CONTRIBUTING.md on collaboration, guidelines,
and assistance.

HYDRASIR-83 #close Reconciling README and CONTRIBUTING

JIRA References:
https://jira.duraspace.org/browse/HYDRASIR-83
Merge pull request #392 from projecthydra/feature/HYDRASIR-83

Refocusing README.md and CONTRIBUTING.md