improve README

[ThomasWaldmann]

see the borgbackup README, elevator speech style.

[gobborg]

Should the rtd homepage's "Edit on Github" link to the borg-import/docs/index.rst instead of the readme?

[ThomasWaldmann]

Guess these links are auto-generated for each page of the docs.

[gobborg]

Can that be fixed? Rtd's /latest is the README.

[ThomasWaldmann]

Not sure it is worth fixing that. Guess people will find the right files anyway.

[lucYang55]

Hey I was wondering if there was anything else that I could do to help improve the read me