Update documentation throughout repo

[spwoodcock]

Replacement of #164

We currently have some minimal documentation, which could be greatly improved.
We would really welcome PRs for this 🙏

What needs to be done:

• Proof reading of current docs and correction.
• Reduce docs duplication - we currently have the same content duplicated in a few places.
• Improve general README, contributors guidelines, etc.
• Improve developer documentation with additional examples, FAQs (if you struggled setting up FMTM anywhere, feel free to document it!).
• Improve user documentation for how to use FMTM.
• Python docstrings throughout the backend, where missing (especially on routes).
• If you particularly like writing JSDoc docstrings, then it wouldn't harm having a few in the frontend too.

[vinayakhegde1]

@spwoodcock I've imrpoved the contributing guidelines please do check