Command Format: command for creating event revised
Command Format: command for creating event revised

1. change the command key word `add` to `event` to be differentiated
   from other kinds of tasks

2. add example description

CS2103AUG2016-T11-C4/main,snehasp13/main,nightism/addressbook-level4,snehasp13/main,nightism/addressbook-level4,CS2103AUG2016-T11-C4/main