docs/projects/ad719x_asdz: Update documentation

 * Added GPIO section as it was missing
 * Added details on using the make parameter ARDZ_PMOD_N as well as
   separate build commands depending on the carrier
 * Removed the diagram from Software considerations as it didn't make
   sense, since the evaluation board which doesn't have PMOD connector will be
   placed on top of Cora to use the Arduino header, and not connected through
   wires
 * Added links to Linux and no-OS files

Signed-off-by: Iulia Moldovan <[email protected]>