Training documentation

Explain what tools we use for logging (Tensorboard) with screenshots.

This will be in a new section Training at the root of the navigation then under a page Logging.

changed milestone to %ML Prod - December 2022 n°1

added P3 label

assigned to @starride

mentioned in issue #10 (closed)

added 1 deleted label

changed milestone to %ML Prod - Next

unassigned @starride

mentioned in merge request !261 (merged)

added Documentation label