Update index.srt

Added details about "Improve this Doc" button and completed the offline options description.
[pt] [2.x] Update index.rst

Added details about "Improve this Doc" button.
Corrected the uppercase mistake in one of the links.
Completed the offline options description.
Merge pull request #1752 from andtxr/patch-1

[pt] [2.x] Update index.srt