I like this idea a lot, but you will cause a lot of people to bounce at step 2. Or at least, that has been my experience over the years. No matter how much you reassure them that it is okay if stuff is confusing and in fact you'd like to know about it so you can fix it, they'll say "great" and then go radio silent 99% of the time.
I feel like for any long-running project, that person is at least ME. If I haven't written down some architectural information for complex projects, when I revisit a project after it being dormant for half year, I need to poke around to figure things out again.
If I have written down architecture notes in the first place, they are very helpful at this point; and if I haven't, it's a good time to start because I'll be acutely aware of the non-obvious parts as I re-familiarize myself with the code.
Sounds right to me too. One quicker way to improve the 'first process' is to change only step one - do not spend a long time, but instead write a few paragraphs with what's most important and/or top-of-mind. Often, this opens the door to more contributions and questions.
Of course, update accordingly whenever you find yourself in a discussion about something with a contributor (no matter if the architecture doc is even part of the discussion or not).
I usually reach for a friend, or someone I've met before, since using the first version of a doc is asking a lot! (And they're often part of the target audience).
