Add initial tags to capability conclusions

[nchan0154]

This PR adds some initial tags to capabilities. Your insights on whether or not I'm on the right track would be appreciated! I wanted to link the Canvas spec as a related specification under 'Display an image file as a map layer', but I'm not super familiar with Respec, so a pointer in the right direction would be helpful.

[AmeliaBR]

Haven't reviewed yet, but on this point:

so a pointer in the right direction would be helpful.

• General overview of referencing in ReSpec
• The short codes for references are in the SpecRef database, which you can also search from your local live copy of the built spec, by clicking on the ReSpec button in the top right.
• If any references come up that aren't in SpecRef, you can define a local ref in the JSON metadata at the top of the file, as part of the localBiblio object. (As that linked doc says, this "is discouraged", and at some point we should take the ones that are already there & submit them to SpecRef. But it works for the time being.)

PS, for Canvas, the reference spec is currently the WHATWG HTML spec. The W3C one is out of date.