Docs navigation update - diagram

[lauracumming]

Summary
Gitbook has grown and become a bit difficult to navigate. We need to consolidate, delete, re-order and re-label in places to help users find things more easily. This task is just to update any navigation maps.

User story
The user story that has led to the need for this task, expressed in the format below.
_As a teacher/student/independent/contributor
_I would like to find the docs that i need
_so that i can complete my task

Outcome/deliverable
What will be the outcome once this task has been completed? What deliverables (documents, posts, decks, emails etc) do you expect/need to be produced?

Deadline
Tbc

Reviewer
@SKairinos @faucomte97

People to contact
@lauracumming