Update to all introductory content--compare with main project website.

[mradamcox]

describe the issue

The Introduction section of the documentation is pretty stale and out of date, and I think a thorough rewrite of it would be very beneficial. One reason is that a lot of content there overlaps with general information that is available on archesproject.org, and I think that the official project website is probably a better place for this info than the docs. So, I think this effort should be made as an evaluation of Arches content between the two locations. for example: There should probably be only one long-form road map/version history. Where should that be located?

Also, as Lindsey mentioned in slack, we need to update the release list, and it would best to link back to the official release notes in the core arches repo, rather than try to duplicate any information here.

which release does this issue concern?

all