Everything here is basic, or core, Markdown and will be supported by any markdown editor. Since Markdown is simply encoding document structure through markup, several different implementations have expanded on this core set and allow you to do other things, including footnotes, references etc.
We'll keep it simple for the moment; this is all you really need for your
_README.md files! Later, you'll be introduced to RMarkdown, which, when used in conjunction with R, will allow you to render statistical analyses within your Markdown document and build reference lists, among other things.