So far the Tobiko docs were duplicated in some places, different
(although duplicated), and some fragments were not relevant (or
outdated).
This patch refactors the Tobiko installation guide by modularizing the
fragments ("spilling" fragments instead of coping them), correcting
typos, and deleting/updating irrelevant information.
Note: in order to see how the change will appear, download it with
`git review -d <change_url>`, run the `tox -e docs` command, and then
double click
(with the file explorer) tobiko/doc/build/html/<file-you-want>.
Change-Id: Ib5ce8a166bb036a5c49a396e568f8bd8b79f6a17
8138c3ff9a