Edit user guide to fix issues

[kevnw]

Issues fixed:

• 156
• 157
• 158
• 159
• 162
• 165
• 171
• 179
• 184
• 185
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• 189

[codecov-io]

Codecov Report

Merging #193 into master will decrease coverage by 0.03%.
The diff coverage is 50.00%.

@@             Coverage Diff              @@
##             master     #193      +/-   ##
============================================
- Coverage     57.37%   57.34%   -0.04%     
- Complexity      771      773       +2     
============================================
  Files           134      135       +1     
  Lines          2942     2949       +7     
  Branches        452      453       +1     
============================================
+ Hits           1688     1691       +3     
- Misses         1076     1079       +3     
- Partials        178      179       +1     

Impacted Files	Coverage Δ	Complexity Δ
...main/java/seedu/address/commons/core/Messages.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
...seedu/address/logic/parser/ClearCommandParser.java	42.85% <42.85%> (ø)	2.00 <2.00> (?)
.../seedu/address/logic/parser/AddressBookParser.java	66.66% <100.00%> (ø)	12.00 <0.00> (ø)

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[luciatirta]

Looks good to merge!