Transformers cli clean command (#37657)

* transformers-cli -> transformers

* Chat command works with positional argument

* update doc references to transformers-cli

* doc headers

* deepspeed

---------

Co-authored-by: Joao Gante <joao@huggingface.co>

CONTRIBUTING.md

@@ -78,7 +78,7 @@ Once you've confirmed the bug hasn't already been reported, please include the f
 To get the OS and software versions automatically, run the following command:
 
 ```bash
-transformers-cli env
+transformers env
 ```
 
 You can also run the same command from the root of the repository: