examples: Clarify install instruction in wolf_sheep

Author: rht

examples/wolf_sheep/Readme.md

@@ -19,6 +19,11 @@ The model is tests and demonstrates several Mesa concepts and features:
 To install the dependencies use pip and the requirements.txt in this directory. e.g.
 
 ```
+    # First, we clone the Mesa repo
+    $ git clone https://github.com/projectmesa/mesa.git
+    $ cd mesa
+    # Then we cd to the example directory
+    $ cd examples/wolf_sheep
     $ pip install -r requirements.txt
 ```