Ug pics

[chunyongg]

• Add more pictures
• Fix some formatting issues
• Add a new section called Layout

Refer to https://chunyongg.github.io/tp/UserGuide.html to see the outcome of this PR.

[codecov-io]

Codecov Report

Merging #200 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #200   +/-   ##
=========================================
  Coverage     48.51%   48.51%           
  Complexity      782      782           
=========================================
  Files           155      155           
  Lines          3865     3865           
  Branches        461      461           
=========================================
  Hits           1875     1875           
  Misses         1853     1853           
  Partials        137      137           

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