minor punctuation fixes - adding missing commas

[shawna-slh]

from @pallabiwrites https://github.com/w3c/wai-intro-wcag/pull/307/files

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[shawna-slh]

i.e. -> i.e.,

comma also needed in Notes in Success Criterion 2.5.1 Pointer Gestures and 2.5.2 Pointer Cancellation

[shawna-slh]

@patrickhlauke did you also take care of

i.e. -> i.e.,
comma also needed in Notes in Success Criterion 2.5.1 Pointer Gestures and 2.5.2 Pointer Cancellation

?

[patrickhlauke]

i only approved the PR, not work on anything further no

[patrickhlauke]

done a few more stragglers. note that there's the same kind of issue with e.g., much more pervasive throughout a LOT of documents. though it may actually be a good idea to take a step back and see if we want to use something nicer, like "for instance" / "for examples" instead, to aid comprehension. but leaving that as an exercise for another day...