MLflow docs tutorial: add instruction about installing scikit-learn (m…

…lflow#1319)

* Install sklearn instruction

* Provide installation options

docs/source/tutorial.rst

@@ -27,7 +27,13 @@ To run this tutorial, you'll need to:
 
     .. container:: python
 
-       - Install MLflow (via ``pip install mlflow``)
+       - Install MLflow and scikit-learn. There are two options for installing these dependencies:
+
+           1. Install MLflow with extra dependencies, including scikit-learn
+              (via ``pip install mlflow[extras]``)
+           2. Install MLflow (via ``pip install mlflow``) and install scikit-learn separately
+              (via ``pip install sckit-learn``)
+
        - Install `conda <https://conda.io/projects/conda/en/latest/user-guide/install/index.html>`_
        - Clone (download) the MLflow repository via ``git clone https://github.com/mlflow/mlflow``
        - ``cd`` into the ``examples`` directory within your clone of MLflow - we'll use this working