Add db client packages to dev env setup doc.

Dev env setup doc hasn't been updated in a while and
needed the addition of the mysql and psql packages.

Tested this on a clean install and it looks like
the addition of these two pkgs should get us up to
date.

Change-Id: I66011478064bd8fb85bfaf56e8b14232226e0efc
Merge "Add db client packages to dev env setup doc."