What would be really nice is if somehow one could hack Github to allow inline commenting on existing code as easily as on a PR or other commit. Then it might be natural to use that UI for the purposes of, say, creating a Github issue.
As it is, without some sort of inline commenting, the barrier to people submitting small corrections/suggestions is much higher. If I have a number of comments on a document, and I want to do it in JIRA or in a Github issue, I have to write my comments in such a way that the references back to the document are at least unambiguous, even if they aren't actually useful in taking the reader straight to the code to be edited. For an LTD document the best way to do this probably would be to copy/paste in the permalinks to section headers provided by the HTML renderer (hover over a section title to see the permalink icon appear next to it).
But this is an order of magnitude more trouble than the use of a natural inline commenting scheme.
Of course, if the commenter is confident enough to actually edit the document, then a PR is the natural vehicle in any event - but even in that case it would be nice to ease the process of also generating a matching JIRA ticket to support the ticket-based workflow of merging the edits to master.
(And if you are now wondering why I didn't just actually edit "enhancement" to "improvement" myself, the answer is that Jonathan Sick and I were deliberately using this as a test case for how to accept comments.)