Install appdata files to /usr/share/metainfo

[sidt4]

$ apt-file search /usr/share/appdata/
fityk: /usr/share/appdata/fityk.appdata.xml

...

• Refer: https://www.freedesktop.org/software/appstream/docs/chap-Metadata.html#spec-component-location
• Refer: https://appstream.debian.org/sid/main/issues/fityk.html
• Refer: https://appstream.debian.org/sid/main/metainfo/fityk.html