Add explanation for installing Python development packages.

Installing software via pip requires the development files
as well. This update simply notes the package names per type
of package being used. Also added a note about extra packages
being possibly needed for building, such as with Tempest.

Partial-Bug: 1367526
Change-Id: I0430c08686012b31073ed98040b5e261a9205ca6
Merge "Add explanation for installing Python development packages."