prod: updated install instructions to include python module dependencies

Author: rhornig

INSTALL.md

@@ -24,15 +24,18 @@ General
 If you are building from command line:
 --------------------------------------
 3. Change to the INET directory and source the `setenv` script.
-   
+
        $ source setenv
 
-4. Type `make makefiles`. This should generate the makefiles for you automatically.
+4. Make sure that any required Python modules are properly installed by executing
+  `pip install -r python/requirements.txt`
+
+5. Type `make makefiles`. This should generate the makefiles for you automatically.
 
-5. Type `make` to build the inet executable (release version). Use `make MODE=debug`
+6. Type `make` to build the inet executable (release version). Use `make MODE=debug`
    to build debug version.
 
-6. You can run specific examples by changing into the example's directory and executing `inet`
+7. You can run specific examples by changing into the example's directory and executing `inet`
 
 If you are using the IDE:
 -------------------------