Bug#840879: rosegarden: Please announce supported hardware using AppStream

[Ted Felix <ted@tedfelix.com>]

Just added this upstream:

https://sourceforge.net/p/rosegarden/git/ci/934201c940081f6d9139f4977768058ec3f0e4e4/

There's already a <provides> tag at the top and I added it (along with 
some documentation) to that instead of at the bottom.  Looks like this now:

    <provides>
      <id>com.rosegardenmusic.rosegarden.desktop</id>
      <!--
           ic01: Interface Class 0x01: AUDIO
           isc03: Interface Sub Class 0x03: MIDISTREAMING
           See "Universal Serial Bus Device Class Definition for Audio
           Devices" at usb.org.
      -->
      <modalias>usb:*ic01isc03ip*</modalias>
    </provides>