ux: remote-viewer is a graphical app

Added a note remembering to the user that remote-viewer is
a graphical application.

Change-Id: Id5e24474546caf3067ad48eab3cdb699e2fa6af6
Bug-Url: https://bugzilla.redhat.com/1001706
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>