Fix documentation bugs

[sgn00]

No description provided.

[codecov-io]

Codecov Report

Merging #168 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #168   +/-   ##
=========================================
  Coverage     64.68%   64.68%           
  Complexity      588      588           
=========================================
  Files           108      108           
  Lines          2005     2005           
  Branches        223      223           
=========================================
  Hits           1297     1297           
  Misses          627      627           
  Partials         81       81           

Impacted Files	Coverage Δ	Complexity Δ
...ava/seedu/flashcard/logic/commands/AddCommand.java	100.00% <ø> (ø)	8.00 <0.00> (ø)
...va/seedu/flashcard/logic/commands/EditCommand.java	96.29% <ø> (ø)	12.00 <0.00> (ø)
.../seedu/flashcard/logic/commands/FilterCommand.java	87.50% <ø> (ø)	7.00 <0.00> (ø)
...va/seedu/flashcard/logic/commands/FindCommand.java	100.00% <ø> (ø)	6.00 <0.00> (ø)
...va/seedu/flashcard/logic/commands/SortCommand.java	100.00% <ø> (ø)	7.00 <0.00> (ø)
...a/seedu/flashcard/logic/commands/StatsCommand.java	100.00% <ø> (ø)	7.00 <0.00> (ø)
...a/seedu/flashcard/logic/commands/UnfavCommand.java	84.61% <ø> (ø)	9.00 <0.00> (ø)
...va/seedu/flashcard/logic/commands/ViewCommand.java	100.00% <ø> (ø)	9.00 <0.00> (ø)
...java/seedu/flashcard/model/flashcard/Category.java	90.00% <ø> (ø)	9.00 <0.00> (ø)
...va/seedu/flashcard/model/flashcard/Statistics.java	78.12% <ø> (ø)	18.00 <0.00> (ø)
... and 1 more

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[minzzelo]

LGTM!