Architecture notes

[Brent Moran]

Hello!

I tidied up my old Architecture notes branch on the wiki, and updated to reflect the current plan. While I'm still going through to try to cut some scope for the Beta launch, I think these notes are at the stage where I'd like some feedback. Particularly, I welcome feedback on the new pages created by this PR. 

I still want to add a page about how we're going to handle types and their installation, but I actually think that can (and probably should) wait until after we release the beta, so I'm not including that in the PR for now.

Brent

[Brent Moran]

I meant to add: Please use the PR review mechanism to provide feedback, if you have any. I'll be requesting review from a few in particular, but all are welcome.

[Kriti Godey]

Thanks, added to my queue to review.