update to developer security training guidance

Why is this change being made?

Adding description and guidance for new security control on secure code training.

How will this merge request impact page speed?

Not sure

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