Add AM3 Run-a-model Docs

[Whyborn]

We need to add AM3 Run-a-model docs before alpha releasing AM3. I am aware that the layout of the landing page is changing, but the docs created should be able to be ported to the new format fairly easily.

[atteggiani]

I see this as a duplicate of #993.
Are you and Ben both working on it and can this be joined together with that?