Add information to existing documentation pages

Why is this change being made?

Add information and links to the existing documentation pages about using Git and command line.

Why? Keep a SSOT and the handbook DRY.

How will this merge request impact page speed?

No

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what