Emacs org-mode is great at producing Taskjuggler charts. The documentation is a bit rough though.

This is the most thorough walkthrough I've found though it uses the QT-based Taskjuggler 2:

https://orgmode.org/worg/org-tutorials/org-taskjuggler.html

This guide goes through the ruby-based TJ3, though it ends kinda abruptly:

https://orgmode.org/worg/exporters/taskjuggler/ox-taskjuggle...