Alt files shoudn't be tracked

[Thaodan]

Is your feature request related to a problem? Please describe.

Yadm allows the use of alt files but it also allows users to antecedently checked in
files that have alt files.

Alt files shouldn't be tracked as the non-alt version of the file would be overridden each time
yadm links the appropriate alt file to the non-alt file.

Describe the solution you'd like

Ask user before they want to add files that are tracked by alt files

Describe alternatives you've considered

An alternative would to gitignore files that have alt files.