Add minor doc-string change to include hp_name param in hyperparameter_search
This is a very minor change. It seems like one of the parameters of the hyperparameter_search method hasn't been documented yet. :slightly_smiling_face: 
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_18700). All of your documentation changes will be reflected on that endpoint.<|||||>Just noticed, that the kwargs- argument is also not displayed correctly. Probably because of the missing type-information:
![image](https://user-images.githubusercontent.com/60255589/185738973-076ed76d-c13a-4058-ab20-8f5c9c37ec0a.png)
<|||||>Better, but still parsing issues. Maybe because of the missing white-space. 
![image](https://user-images.githubusercontent.com/60255589/185740453-94cd44cf-4a73-497f-b5b6-142813578df6.png)
<|||||>Yes, that did the trick. Now it looks alright. 

![image](https://user-images.githubusercontent.com/60255589/185742902-cc653820-325c-4861-ac0f-ea6c5310cf87.png)
