Add timm to requirements

[marcozullich]

Some scripts, like transfer_weights.py require the library timm. It should be added to requirements.txt

[FrancescoSaverioZuppichini]

Hi @marcozullich, I hope to find you well. The scripts are not meant to be run by the end-user. But in my setup.py I am using find_packages so if I remember correctly I am skipping the requirements file. I'll have to check it, but yeah, if setup.py is not calling the requirements.txt then there is not risk in adding timm there :)