Add rST on setting up Dox

Add instructions on setting up the testing environment and the command
environment necessary to generate the Dox pages locally.

Add section on the README for the instructions.

OSEHRA-Id: http://issues.osehra.org/browse/OAT-158
Change-Id: I44a5b16e82f238aabd16e3064eaf7ef4dd272014