fix addon broken links in documentation

[mnicole]

Issue:

What I did

• Fixed a few broken links in the documentation for the add on pages (introduction and using add ons)

How to test

• Click on the links :)

[shilman]

Thanks for your fix!! 🙇

[codecov]

Codecov Report

Merging #1165 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1165   +/-   ##
=======================================
  Coverage   12.72%   12.72%           
=======================================
  Files         199      199           
  Lines        4582     4582           
  Branches      727      727           
=======================================
  Hits          583      583           
  Misses       3356     3356           
  Partials      643      643

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