docs: verify/bisect: use git switch, tag kernel, and various fixes

Various small improvements and fixes:

* Use the more modern 'git switch' instead of 'git checkout', which
  makes it more obvious what's happening (among others due to the
  --discard-changes parameter that is more clear than --force).

* Provide a hint how a mainline version number and one from a stable
  series look like.

* When trying to validate the bisection result with a revert, add a
  special tag to facilitate the identification.

* Sync version numbers used in various examples for consistency: stick
  to 6.0.13, 6.0.15, and 6.1.5.

* Fix a few typos and oddities.

Signed-off-by: Thorsten Leemhuis <linux@leemhuis.info>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/85029aa004447b0eeb5043fb014630f2acafacec.1712647788.git.linux@leemhuis.info