fix(docs): add a build.tools.python entry

Specifying build.tools is mandatory. We use python, so use the latest
one available. For ubuntu 22.04 that should be 3.10 or thereabouts.

Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
Change-Id: Ifd184b9f3b2d8e91182ccb73c47b148e4aeaff05