Change "Usage Documentation" to "User documentation"

[theking2]

No description provided.

[i2h3]

@theking2 Hi! Can you please write at least something in the pull request description to explain it?

[theking2]

The commit-text and PR title is quite elaborate.
The PR request a change of "Usage Documentation" to "User Documentation". Usage Documentation is not proper english or one could gracefully interpret it as the documentation of how the software was used, not how to use it.