Add docs for qml.ftqc module

[joeycarter]

Adds the qml.ftqc module to the docs index so that Sphinx captures the documentation therein.

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit doc/releases/changelog-dev.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
• Your name (or GitHub username) in the contributors section.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.60%. Comparing base (2c3a11f) to head (f5e5b52).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7018   +/-   ##
=======================================
  Coverage   99.60%   99.60%           
=======================================
  Files         484      484           
  Lines       46249    46249           
=======================================
  Hits        46065    46065           
  Misses        184      184           

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[JerryChen97]

lgtm