Merge pull request mlflow#23 from harupy/fix-pip-install

Fix `pip install` command

README.md

@@ -27,7 +27,7 @@ Your contribution to MLflow Recipes is greatly appreciated by the community!
 To use MLflow Recipes in this example repository,
 simply install the packages listed in the `requirements.txt` file. Note that `Python 3.8` or above is recommended.
 ```
-pip install requirements.txt
+pip install -r requirements.txt
 ```
 
 You may need to install additional libraries for extra features: