Update handbook to make it clearer on how to connect with other team members

Creating this issue as a follow-up to this comment thread on the FY23-Q3 Visiting Grant Program MR.

As a first iteration I'll put together a handbook page/section as @drogozinski suggests:

it sounds like a great next step to add a handbook section about finding team members in your area. Adding all combined suggestions, plus a directory of #loc_* channels. Key question is where it lives, but I suspect we can find the right home for it.

Does anyone have any thoughts on where this section or page should live? I tried searching the handbook for similar content and wasn't finding a home that made 💯% sense to me.

I'll ask #it_help if it's possible to easily get a list of all Slack channels of the form #loc_* and their descriptions.

cc: @tmccaslin @cablett @epetoskey @beckalippert @drogozinski