Meta: add "Discussions" to GitHub repo?

[GregVernon]

I didn't see any forum or other community location for discussion / general Q&A for SMT listed on the project website. Various other open-source projects have enabled GitHub Discussions for their GitHub-based repositories and I thought maybe SMT might consider doing so too.

Examples:

• MOOSE: https://github.com/idaholab/moose/discussions
• Dakota: https://github.com/orgs/snl-dakota/discussions
• Firedrake: https://github.com/firedrakeproject/firedrake/discussions

[relf]

Ok, it's enabled now.