Add date parameter guidelines to UG

[chiangqinkang]

Resolves #142

[codecov]

Codecov Report

Attention: Patch coverage is 77.91878% with 174 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../address/logic/commands/AddAppointmentCommand.java	38.63%	26 Missing and 1 partial ⚠️
src/main/java/seedu/address/ui/PatientCard.java	0.00%	25 Missing ⚠️
src/main/java/seedu/address/ui/DoctorCard.java	0.00%	24 Missing ⚠️
src/main/java/seedu/address/logic/Messages.java	0.00%	11 Missing ⚠️
...a/seedu/address/model/appointment/Appointment.java	87.69%	0 Missing and 8 partials ⚠️
...dress/model/appointment/UniqueAppointmentList.java	82.60%	4 Missing and 4 partials ⚠️
...s/logic/parser/DeleteAppointmentCommandParser.java	36.36%	7 Missing ⚠️
...rc/main/java/seedu/address/model/ModelManager.java	0.00%	7 Missing ⚠️
.../java/seedu/address/model/util/SampleDataUtil.java	63.15%	7 Missing ⚠️
...in/java/seedu/address/commons/util/StringUtil.java	40.00%	5 Missing and 1 partial ⚠️
... and 15 more

Files with missing lines	Coverage Δ	Complexity Δ
...seedu/address/logic/commands/AddDoctorCommand.java	100.00% <100.00%> (ø)	8.00 <2.00> (?)
...eedu/address/logic/commands/AddPatientCommand.java	100.00% <100.00%> (ø)	8.00 <8.00> (?)
...dress/logic/commands/DeleteAppointmentCommand.java	100.00% <100.00%> (ø)	6.00 <6.00> (?)
...du/address/logic/commands/DeleteDoctorCommand.java	100.00% <100.00%> (ø)	6.00 <6.00> (?)
...u/address/logic/commands/DeletePatientCommand.java	100.00% <100.00%> (ø)	6.00 <6.00> (?)
...eedu/address/logic/commands/FindDoctorCommand.java	81.25% <100.00%> (ø)	5.00 <1.00> (?)
...edu/address/logic/commands/FindPatientCommand.java	81.25% <100.00%> (ø)	5.00 <1.00> (?)
...u/address/logic/parser/AddDoctorCommandParser.java	100.00% <100.00%> (ø)	5.00 <1.00> (?)
.../address/logic/parser/AddPatientCommandParser.java	100.00% <100.00%> (ø)	5.00 <5.00> (?)
...ain/java/seedu/address/logic/parser/CliSyntax.java	92.30% <100.00%> (+8.97%)	1.00 <0.00> (ø)
... and 44 more

... and 6 files with indirect coverage changes