feat: Add Remark command

[HugeNoob]

Add a new Remark command to complete #10.

I definitely did this myself and did not copy from https://nus-cs2103-ay2324s1.github.io/tp/tutorials/AddRemark.html.

[codecov]

Codecov Report

Merging #15 (901cae2) into master (9242d8d) will increase coverage by 0.68%.
The diff coverage is 86.95%.

@@             Coverage Diff              @@
##             master      #15      +/-   ##
============================================
+ Coverage     75.26%   75.95%   +0.68%     
- Complexity      419      440      +21     
============================================
  Files            71       74       +3     
  Lines          1338     1393      +55     
  Branches        126      132       +6     
============================================
+ Hits           1007     1058      +51     
- Misses          301      304       +3     
- Partials         30       31       +1     

Files Changed	Coverage Δ
.../seedu/address/logic/parser/AddressBookParser.java	90.47% <0.00%> (-9.53%)	⬇️
src/main/java/seedu/address/ui/PersonCard.java	0.00% <0.00%> (ø)
.../java/seedu/address/model/util/SampleDataUtil.java	25.00% <14.28%> (+5.00%)	⬆️
...c/main/java/seedu/address/model/person/Remark.java	87.50% <87.50%> (ø)
...java/seedu/address/logic/commands/EditCommand.java	97.50% <100.00%> (+0.06%)	⬆️
...va/seedu/address/logic/commands/RemarkCommand.java	100.00% <100.00%> (ø)
...a/seedu/address/logic/parser/AddCommandParser.java	100.00% <100.00%> (ø)
...ain/java/seedu/address/logic/parser/CliSyntax.java	85.71% <100.00%> (+2.38%)	⬆️
...eedu/address/logic/parser/RemarkCommandParser.java	100.00% <100.00%> (ø)
...c/main/java/seedu/address/model/person/Person.java	97.43% <100.00%> (+0.21%)	⬆️
... and 1 more

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