[PE-D] `help` command issues

[lctxct]

Missing command descriptions

• [x] https://github.com/AY2324S1-CS2113T-W11-2/tp/issues/156
• [x] https://github.com/AY2324S1-CS2113T-W11-2/tp/issues/160
• [x] https://github.com/AY2324S1-CS2113T-W11-2/tp/issues/161
• [x] https://github.com/AY2324S1-CS2113T-W11-2/tp/issues/171

Others

• [x] https://github.com/AY2324S1-CS2113T-W11-2/tp/issues/158, https://github.com/AY2324S1-CS2113T-W11-2/tp/issues/175

[imaginarys96]

first and third issue are the same. resolved in 75355ac7c270ef78df951420c0eb6f4eb70023c0

[woodenclock]

Fixed the last issue