Missing link in docs fixed

[janosmurai]

Type Of Change

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Any modification in the test cases
• Any modification in the documentation

Checklist:

• I have read and followed the contribution guideline.
• I have checked to ensure there aren't other open Pull Requests for the same update/change.
• All the test cases pass and new modifications in the production code are 100% covered.
• I have made corresponding changes to the documentation.

Related Issue

Closing:
DEM-303

Description

The add-reg command usage changed, so the reference in the navigation bar had
to be updated.

How Has This Been Tested?

The website has been generated with mkdocs on Ubuntu 22.04. The functionality
was tested on the generated website.