Bug#911327: add .libretro metadata for better integration with gnome-games

[Patrick Ammann]

Package: libretro-mgba
Version: 0.6.3+dfsg1-2


Please consider adding .libretro metadata for better integration with 
gnome-games.


See 
https://gitlab.gnome.org/GNOME/gnome-games/blob/master/flatpak/libretro-cores/mgba.libretro:
<snip>
[Libretro]
Type=Emulator
Version=1.0
Name=mGBA
Module=mgba_libretro.so
LibretroVersion=1
Authors=Jeffrey Pfau;
License=MPL-2.0;

[Platform:GameBoyAdvance]
MimeType=application/x-gba-rom;
Firmwares=GameBoyAdvance;

[Firmware:GameBoyAdvance]
Path=gba_bios.bin
MD5=a860e8c0b6d573d191e4ec7db1b1e4f6
Mandatory=false
</snip>

The file mgba.libretro is expected to be here 
"/usr/lib/x86_64-linux-gnu/libretro/"


Thanks,
Patrick