Adding more info about using user-testing templates and a link to where to find it on the handbook

Why is this change being made?

To bring more transparency to the team and newcomers, it's a good idea to add how/where using a template could speed up our work with unmoderated user testing. We discussed this on slack, and we couldn't find anything about this in the handbook.

I find it extremely fast to use a template when launching an unmoderated testing study, it would be good to have this information in the handbook.

I have added as a last item on Frequently Asked Questions

• Do we have a template I could use to quick start my study? Yes, check out account templates and choose one from there.

Related to gitlab-org/ux-research#2410 (closed)

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