Wrong command example for `add patient` and `add a patient visit` in command summary

[JordanKwua]

The adding of a patient's visit example does not match the format (n/ is in example but not in format)

same for the adding of a patient example

Command for adding of a patient is also very different from the given format in the command summary

[nus-se-bot]

Your response not required for this bug as the team has accepted the bug as it is.