Documentation/11/update gh pages

[helen-d-little]

Re-ordering of documentation and running simulation ipynb added. Contributes to #2 #11 from ground control REG

[radka-j]

Looking great! I think the main issue we have is that we are still waiting for the overall infrastructure to stabilise a little bit (e.g., the About page is likely to change quite a lot but there is no point in trying to second guess that now).

Some minor points/comments/questions:

• there are references to Simurgh throughout, I'd remove those since the aim is to not use that repo anymore (although this might mean some sections need rethinking)
• in the command reference section, should the BlueBird page link to the BlueBird API doc: https://github.com/project-bluebird/bluebird/blob/master/API.md ?
• installation instructions and the running an airspace simulation notebook currently do pretty much the same - (i) I'd separate "installation" from "usage" (or something like that) and (ii) it is possible that your command line instructions are better than a notebook if we can't interact with the notebook so maybe we just remove that for now (what do you think) ??