UserGuide: wrap `edit-event` command definition
UserGuide: wrap `edit-event` command definition

It was going off the side of the page.

As a general rule, everything should be wrapped at 80-characters.

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