## Summary
Add `installer` method to `InstalledDist` to distinguish between
different installers. Might be nice to add an enum for all possible
installers, but this might be too hard to keep up to date :).
The `INSTALLER` file is a file that can be added to the `.dist-info`
folder with the installer name.
Closes: #1759
## Test Plan
Not sure if there is a place I can automatically test it, if you have a
pointer I would be happy to add a test.
Tim de Jager
8cbeab7107