Support for Markdown files

[tdudgeon]

We need to support the ability for users to document their work in projects.
A simple way of handling Markdown files, and special treatment of README.md in a way similar to how GitHub does this would go a long way towards this.

Need to be able to:

• display formatted Markdown files in a viewer
• if a README.md file is present then display it's contents as part of the directory listing
• allow to edit Markdown files
• allow to incorporate links to other files in the project (and external URLs) into the Markdown content

[OliverDudgeon]

Display of markdown should be quite easy since we already display mdx files
Editing is more difficult but is possible via Jupyter currently

[tdudgeon]

Yes, editing can be done in Jupyter for now, but I bet there's a library that we can use that allows this.

[OliverDudgeon]

Yes, the engine behind VSCode can be deployed which supports a lot of stuff including markdown.