Rewrote the user guide section about the settings dialog (#14937)
Fixes #14927
Summary of the issue:
The issue asked that Ctrl+Tab and Shift+Ctrl+Tab be listed in the user guide section regarding the settings dialog, since many users don't know they can use those to move between categories.
Description of user facing changes
While editing the section, I found some awkward and seemingly redundant wording, and some unclear portions.
Reworded the initial paragraph to be more clear about categories and settings.
Added a note that Ctrl+Tab and Shift+Ctrl+Tab can move between settings categories.
Clarified a sentence about what shortcut keys for categories do.
Made the note about adding shortcut keys for categories more clear. As it was written previously, it implied that adding shortcut keys might be the ONLY way to access those categories.
