Make it clearer that watching the security videos is optional

Why is this change being made?

I missed security training the first time around, and am only just catching up. In general, I find the videos very unapproachable.

I prefer to digest this kind of information in text form, but the way the page is worded at the moment, it feels like watching at least some of the videos is mandatory, which probably isn't intentional.

This MR reorders some recommendations and softens them a bit so we give equal preference to "watch the video" vs "read the slides". If there are specific parts of the video that we think should be mandatory viewing, we can always call those out explicitly - or add additional resources alongside the slides to make watching the video optional..

Does this MR meet the acceptance criteria?

Conformity

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