Update third-party archetypes list

[nuclearkatie]

I think we should probably update the third-party archetypes list on the user guide. A couple possible changes/additions:

• mbmore points to @mbmcgarry's repo, I think it should point to cnerg/mbmore at this point since that is the repo with active development @bam241
• mbmore:CascadeEnrich is probably to the point where it can be listed under mbmore
• Not sure if we should add any of the ARFC-developed archetypes, like pyre or d3ploy. Thoughts @katyhuff ?
• ... anything else?

[nuclearkatie]

I think I could probably kill several birds with one PR here.

• Move third-party archetypes to a new page, as proposed in Third Party Archetypes #266
• Add new mbmore archetypes, including the ones @mbmcgarry tried to add in Mbmore updates #233 (which I didn't even list before)
• add any other new archetypes
• would also close Add page of links to known archetypes, their docs, and repos #123

[gonuke]

This is a good plan. Not sure if it should be a single PR or a series of PRs so that we can review the implementation of each of these steps separately?