Add note to AMS bootloader installation about OF file.

Some devices contain a bin file in the root folder of the player. This caused
confusion a couple of times, since the installer asks for a bin file. Add a
note that the required file is not present on the player and will get removed
automatically.

Change-Id: I6cd5c25b319770555c3939377a3ed86ed3181dad

rbutil/rbutilqt/base/bootloaderinstallams.cpp

@@ -40,6 +40,8 @@ QString BootloaderInstallAms::ofHint()
               "<a href='http://www.rockbox.org/manual.shtml'>manual</a> and "
               "the <a href='http://www.rockbox.org/wiki/SansaAMS'>SansaAMS</a> "
               "wiki page on how to obtain this file.<br/>"
+              "<b>Note:</b> This file is not present on your player and will "
+              "disappear automatically after installing it.<br/><br/>"
               "Press Ok to continue and browse your computer for the firmware "
               "file.");
 }