improve PR message on new member added workflow

[afewell]

User Story: after registering with the community, new members should be notified with clear messaging that provides information on getting started with the community

Proposal: The current PR message posted after the new member added workflow runs does not currently provide sufficient detail to help direct new members with clear next steps for learning about member features and common use cases for new members. Update the current message with additional details and links to key resources. The message should still not be lengthy, and should include a link to the ModernApps Skills 101 course, and if needed a new page could be created to provide a consolidated list (quick start guide) for new members. The message should continue to include links to the members modernappsninjas repo and site.