Update metainfo so app shows as mobile friendly in Flathub

[radmorecameron]

Follow up to #69 . This change will allow the app to show up in https://flathub.org/en/apps/collection/mobile/

This can be checked using: appstreamcli check-syscompat ./data/com.ranfdev.DistroShelf.metainfo.xml.in

Before:

Chassis compatibility check for: */*/*/com.ranfdev.DistroShelf/*

Desktop:
 ✔ Compatible (100%)

Laptop:
 ✔ Compatible (100%)

Server:
 ✘ Incompatible

Tablet:
 ✘ Incompatible

Handset:
 ✘ Incompatible

After:

Chassis compatibility check for: */*/*/com.ranfdev.DistroShelf/*

Desktop:
 ✔ Compatible (100%)

Laptop:
 ✔ Compatible (100%)

Server:
 ✘ Incompatible

Tablet:
 ✔ Compatible (100%)

Handset:
 ✔ Compatible (100%)

[ranfdev]

Thank you!