Roles page - updates

[writerly03]

• [x] Add in that lead is responsible for tracking hours
• [x] Add in Operations Role; note that internal hours are managed by this person
• [ ] Make more substantive edits to role descriptions to ensure they're accurate. Aim of this page is to describe roles as they are ideally for the purpose of succession planning; not as they are now if actual operations vary.

[writerly03]

I still need to do a first pass at editing; @benhylau to update more substantively once I'm done.

[LexaMichaelides]

Closing in favour of https://github.com/hyphacoop/organizing-private/issues/247