Move from readme to readthedocs

[14renus]

Shorted README on github page and link to readthedocs documentation instead.
Move documentation to user guide on readthedocs.

Other improvements:

• Add documentation on hydra arguemtns.
• Put ArchesWeather in its own section.
• Recommend better practice for forking repo and creating dev branches rather than having all dev branches on public repo (gets crowded)

Fix #8