Create Online Markdown Files
There are different possibilities in order to create online markdown files.
Repository Stack
Repository Stack and its online text editing capabilities comes with an option for markdown syntaxt. This makes it easy for editing and creating text and markdown files with any browser on mobile or desktop.
Integrated FTP Text Editor
There are several FTP clients available for macOS (like Transmit or Cyberduck) or iOS (like FileBrowser or FTPManager) with integrated text editor allowing you to create and edit text files on your server.
Markdown Editor
There are several markdown editors available for macOS or iOS like iA Writer which let you create and edit markdown files. In combination with a FTP application you are able to sync these with a FTP server.