.md is registered for Markdown by default. To change the syntax mode for an extension, open a file with that extension, tap the file name in the top toolbar, tap on the "Aa" button, select "Syntax Mode", and change it to the syntax mode you want.
Welcome!
This is the community forum for my apps Pythonista and Editorial.
For individual support questions, you can also send an email. If you have a very short question or just want to say hello — I'm @olemoritz on Twitter.