Improve instructions:
- Reworked configuration section into overview.
- Split CI etup from kickstart.
- Add explanation to run EC2 instances from the web interface.
- Add known limitation section.
- Add architecture diagram
- Add source code overview.
- Add known limitation section.
- Fix MArkdown rendering and typo

Signed-off-by: Vincent Coubard <vincent.coubard@arm.com>