Add option to automatically analyze a file, watching for when it was changed.

[Faalagorn]

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

Without #367 it would be nice if one file (a screenshot) that could be overwritten each time a screenshot is taken would automatically cause the file to be analyzed.

Describe the solution you'd like

Automatically analyze a file that is changed, with some (ideally configurable) file change time threshold.

Describe alternatives you've considered

#367

Additional context

None.