[#660] Update AboutUs.adoc (#661)
[#660] Update AboutUs.adoc (#661)

The AboutUs page has a different format compared to other versions of
AddressBook.

This is untidy.

Let's convert AddressBook - Level4's AboutUs page to be of the same
format as that of other versions of AddressBook. Also, as this project
is expected to be forked and worked on by students, let's also add a
sample page format by updating existing names and images to use
placeholder names and images.
se-edu/addressbook-level3,CS2103R-Eugene-Peh/addressbook-level4,damithc/addressbook-level4,CS2103R-Eugene-Peh/addressbook-level4,CS2103R-Eugene-Peh/addressbook-level4,damithc/addressbook-level4,damithc/addressbook-level4