UG: address vetting comments

[Silvernitro]

• Address vetting comments
• Italicize UI component names in Add command and feature summary list
• Add Clear command

https://silvernitro.github.io/tp/UserGuide.html

[codecov-io]

Codecov Report

Merging #216 (b9daa4f) into master (f2a1d2a) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #216   +/-   ##
=========================================
  Coverage     81.68%   81.68%           
  Complexity      650      650           
=========================================
  Files            96       96           
  Lines          1780     1780           
  Branches        185      185           
=========================================
  Hits           1454     1454           
  Misses          255      255           
  Partials         71       71           

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[yan-soon]

LGTM!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!1