The official documentation format for TF-M is becoming Restructured
Text. This change converts the existing .md files to the new format.

Due to support for documentation of external code (/lib) md support is
kept.

Change-Id: I3c1aef5d22442e0c7c362a40a8d344a266dc0940
Signed-off-by: Gyorgy Szing <Gyorgy.Szing@arm.com>

Adding md files for user guides and licensing.
Using tables in md files requires breaking the 80 column limit.

Change-Id: I97a312e1adb5a36229fe2d806ccca6c7081edc85
Signed-off-by: Abhishek Pandit <Abhishek.Pandit@arm.com>
Co-Authored-By: Marc Moreno Berengue <marc.morenoberengue@arm.com>
Co-Authored-By: Gyorgy Szing <gyorgy.szing@arm.com>
Co-Authored-By: Antonio de Angelis <antonio.deangelis@arm.com>