Backbone/model weights source should be more obvious to figure out.

I saw torchvision in the requirements and immediately assumed that the pre-trained model weights would come from there (I didn’t know timm until very recently).

I saw they are actually coming from timm and realized it’s not a well documented information.

I have two suggestions:

1. (easy) mention it in the readme.md and add it to the docs.

2. (maybe easy?) make the pre-trained weights source a parameter that would show up in the config file (it could come from torchvision for instance)

[jpcbertoldo]

Ok, so just some documentation update.

[samet-akcay]

Addressed with #576