Move doc to index.org, generate index.html serve as GH pages.

[brettviren]

Hi! Thanks for this refcard! I went looking for an online copy and couldn't find one. I think it is a good idea to serve a copy of the exported HTML as a GH page associated with your repository. I put a temporary copy online just to show the goal:

https://brettviren.github.io/refcard-org-mode/

project settings -> github pages -> source -> master / (root) -> save.

And, README.org content needs to move into index.org or otherwise arrange to generate to index.html.

README.org now only holds a few links and probably deserves some more spice. If you accept this PR, best then remove the link to my temporary online copy.

Some minor refcard content was modified:

• Switched to online SETUPFILE. Maybe better to carry a copy of readtheorg?

• I had problems related to id: and had to switch a reference to use the headline text.

• Pointed UP and HOME to links related to the refcard served under "fniessen" namespaces.

[fniessen]

Dear @brettviren , thank you very much for this PR. Very interesting!

One response: Good you switched to the online SETUPFILE -- could be equally local, but this is better to avoid duplicates / out-of-date files.

Dunno why you had problems with ID... Any idea?

Finally, one question: do you know why the TOC is not expanding the nodes when you're scrolling down in the refcard? Locally, that does work...

Happy to merge soon, maybe when that last question would be answered.