Update README to make virtualenv use more clear

Author: Renzo Lucioni

README.md

@@ -23,36 +23,50 @@ All of the services can be run by following the steps below. Note that since we
 configure Docker with a sufficient amount of resources. Our testing found that [configuring Docker for Mac](https://docs.docker.com/docker-for-mac/#/advanced)
  with 2 CPUs and 4GB of memory works well.
 
-1. The Docker Compose file mounts a host volume for each service's executing code. The host directory is expected to be
+1. Create a Python 3 `virtualenv`. If you're using [virtualenvwrapper](https://virtualenvwrapper.readthedocs.io
+), you can do this with:
+
+  ```
+  $ mkvirtualenv devstack --python=$(which python3)
+  ```
+
+  Source the virtualenv and install requirements:
+
+  ```
+  $ workon devstack
+  (devstack)$ make requirements
+  ```
+
+2. The Docker Compose file mounts a host volume for each service's executing code. The host directory is expected to be
    a sibling of this directory. For example, if this repo is cloned to `~/workspace/devstack`, host volumes will be
    expected in `~/workspace/course-discovery`, `~/workspace/ecommerce`, etc. These repos can be cloned with the command
    below.
 
-   ```
-   $ make clone
-   ```
+  ```
+  (devstack)$ make clone
+  ```
 
-2. Run the provision command, if you haven't already, to configure the various services with super-users (for
+3. Run the provision command, if you haven't already, to configure the various services with super-users (for
    development without the auth service) and tenants (for multi-tenancy).
 
    The username and password for the superusers are both "edx". You can access the services directly via Django admin
    at the `/admin/` path, or login via single sign-on at `/login/`.
 
-    ```
-    $ make devstack.provision
-    ```
+   ```
+   (devstack)$ make devstack.provision
+   ```
 
-3. Start the services.
+4. Start the services.
 
     ```
-    $ make devstack.start
+    (devstack)$ make devstack.start
     ```
 
 After the services have started, if you need shell access to one of the services, run `make devstack.open.<service>`.
 For example to access the Catalog/Course Discovery Service, you can run:
 
 ```
-$ make devstack.open.discovery
+(devstack)$ make devstack.open.discovery
 ```
 
 ## Remaining Work