www/hedgedoc: Add new port

The best platform to write and share markdown.

HedgeDoc (formerly known as CodiMD) is an open-source, web-based,
self-hosted, collaborative markdown editor.

You can use it to easily collaborate on notes, graphs and even
presentations in real-time. All you need to do is to share your
note-link to your co-workers and they're ready to go.

...

This brings back www/hedgedoc which was removed a while back because of
the node.js version on tree.