docs: Update requirements.

The list of required packages was not complete. So add all packages we have
forgotten to the requirements list.

Change-Id: Iee178625e9c9027d20bb928241d3bb0afb5619f7
Signed-off-by: Soeren Grunewald <soeren.grunewald@avionic-design.de>
Reviewed-on: http://review.adnet.avionic-design.de/564
Reviewed-by: Hendrik Lippek <hendrik.lippek@avionic-design.de>
build: Use readlink to receive absolute path.

Change-Id: I43f017460daac1de00b65f7f19ecf22f3c279609
Signed-off-by: Soeren Grunewald <soeren.grunewald@avionic-design.de>
Reviewed-on: http://review.adnet.avionic-design.de/567
Reviewed-by: Hendrik Lippek <hendrik.lippek@avionic-design.de>