install appdata to metainfo

from https://www.freedesktop.org/software/appstream/docs/chap-Metadata.html#spec-component-location :

 Upstream projects can ship one or more metainfo files in /usr/share/
Added screenshot to the README
Fixed crash in image creation
Bumped version to 0.3.0
Made create function work
Disable listbox selections
Patched up desktop file
Added icon and policykit styling
Added checkmarks
Support mounting
Initial commit