Update doc for 5.6

[MarceloSalazar]

There are references to mbed OS 5.4 and CLI 1.0.0 (which are very old now).
@Patater please have a look to the markdown doc and update what you consider necessary for the 5.6 release (to be done in a branch).

Update: same applies to other uvisor examples.

[ciarmcom]

ARM Internal Ref: IOTSEC-441