You can also do this directly through Github's normal interface, as creating new markdown files through it is as easy as hitting the add file button and then naming the file ending in md. It also supports dragging and dropping files (the file has to have the markdown file extension added before it'll accept drag and drops btw). Super useful on iPads where vscode's editor can be a little cumbersome.
That is super neat! I had no idea pressing '.' would trigger a web based VS Code to spawn open with files from my selected repo in it. Such a time saver for quick edits compared to the regular single file GitHub file editor.