Add man command

[zaidansani]

Help command requires user to open a man command.

Let's implement a command similar to the man command which shows the message usage.

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 18 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../java/seedu/address/logic/commands/ManCommand.java	25.00%	13 Missing and 2 partials ⚠️
...a/seedu/address/logic/parser/ManCommandParser.java	50.00%	2 Missing and 1 partial ⚠️

Files with missing lines	Coverage Δ	Complexity Δ
.../seedu/address/logic/parser/AddressBookParser.java	100.00% <100.00%> (ø)	13.00 <0.00> (+1.00)
...a/seedu/address/logic/parser/ManCommandParser.java	50.00% <50.00%> (ø)	2.00 <2.00> (?)
.../java/seedu/address/logic/commands/ManCommand.java	25.00% <25.00%> (ø)	2.00 <2.00> (?)