Fix add model like 
It seems that `pip show` does not return the same location as before for editable packages.

However, listing editable packages (`pip list -e`) returns the correct location in which it was installed. Doing it locally returns the following:

```
Package      Version     Editable project location
------------ ----------- ---------------------------------------------
transformers 4.22.0.dev0 /home/lysandre/Workspaces/python/transformers
```

I'm therefore updating the way to identify if we're looking at the correct install to use `pip list -e` instead of `pip show`.
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_18834). All of your documentation changes will be reflected on that endpoint.