Update docs/README.md (#16333)

* Update docs/README.md
Co-authored-by: Lysandre Debut <lysandre@huggingface.co>
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

docs/README.md

@@ -349,6 +349,13 @@ You will first need to run the following command (from the root of the repositor
 python utils/prepare_for_doc_test.py src docs
 ```
 
+If you work on a specific python module, say `modeling_wav2vec2.py`, you can run the command as follows (to avoid the unnecessary temporary changes in irrelevant files):
+
+```bash
+python utils/prepare_for_doc_test.py src/transformers/utils/doc.py src/transformers/models/wav2vec2/modeling_wav2vec2.py
+```
+(`utils/doc.py` should always be included)
+
 Then you can run all the tests in the docstrings of a given file with the following command, here is how we test the modeling file of Wav2Vec2 for instance:
 
 ```bash