Add a link to drush.org in the list on the project page

Problem/Motivation

Trying to find the Drush documentation.

Steps to reproduce

Look every where on the project page. No luck.

Proposed resolution

Add a link "Documentation" to the list on the project page pointing to https://www.drush.org/

In addition/optionally, edit the project meta data under "Resources" and "Documentation" pointing to https://www.drush.org/

Remaining tasks

User interface changes

API changes

Data model changes