Bottom of here for how to add a bunch of images quickly to a gist.
the question here illustrates a way that works always to place images into markdown gists, follow the link through to here to see it in action. Note that the full link extracted from the url seen when viewing the 'raw' image for a gist, a.k.a., "the hard way" on that page, is the only way that really works.
For adding small icons and symbols use advice here to add things like play button [►], etc. and here and here seems good for getting the codes or copying and pasting the symbols themselves, example ◑. Even colored ones --> 🔴.
For sharing markdown-formatted gists in nice format, I found here or here. (I wonder if like nbviewer these could be used to work around occaisions where the markdown viewer in github repos/gists fails. I had at least one case of this where a very long jupyter notebook file fails to load in the viewer that github now includes inside repos and while I have not seen the same phenomena for markdown yet, it is something to keep in mind.)
