Add banner to top of techniques pages, tweak boxout content about techniques

[patrickhlauke]

As I constantly find myself having to explain to some folks that techniques are just informative (the amount of times I had to explain that even if a site doesn't use a particular documented technique, that's fine as long as the actual ask of the success criterion has been satisfied), this adds a standard boxout/disclaimer/note at the top of all techniques pages. This should catch folks who just "stumble" directly across a technique (from a search engine result or similar).

To go with it, this also expands the explanation given in the existing boxouts on the techniques index page and the about page.

Closes #1567

Previews:

• the top of the techniques index page "Summary" boxout https://deploy-preview-5002--wcag2.netlify.app/techniques/
  • Diff from current index
• ditto at the top of the "About techniques" page https://deploy-preview-5002--wcag2.netlify.app/techniques/about
  • Diff from current About page
• random example of one of the techniques (the boxout is the same on all of them) https://deploy-preview-5002--wcag2.netlify.app/techniques/aria/aria1

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[patrickhlauke]

Happy to iterate on this further, but this is a first naive implementation to get a better feel/idea of how it could work/look. Keeping in mind that we (well, > I <) do want it to be quite prominent to catch exactly those folks who don't read things, jump to a technique, and make wrong assumptions about what the purpose of techniques is...

[yatil]

While my preference would be to not have techniques at all (but that is probably a ship that has sailed), a strong warning is a good compromise. I think one could bold “Techniques are examples”.

[alastc]

How about adding this to the bottom of the "About this Technique" box:
"Techniques are examples, they may go beyond the minimum requirement of the criterion, and there may be other ways of meeting the criterion."

[patrickhlauke]

Discussed in TF meeting. Will try to streamline the sentence and add it to the techniques' "About" box, as suggested, and to rework the addition in the "About techniques" boxout (move the extra prose further down in the page rather than in the boxout)