add step 3

dash-apm-python/index.json

@@ -10,6 +10,10 @@
       {
         "title": "Get traces flowing",
         "text": "step_2.md"
+      },
+      {
+        "title": "Enable trace analytics",
+        "text": "step_3.md"
       }
     ],
     "intro": {

dash-apm-python/step_2.md

@@ -1,6 +1,8 @@
 To start all the services run the following, replacing `<KEY>` with your Datadog API key:
 
-`DD_API_KEY=<KEY> docker-compose up`{{copy}}
+`export DD_API_KEY=<KEY>`{{copy}}
+
+`docker-compose up`{{execute}}
 
 Open the web interface to verify the application is up and running:
 

dash-apm-python/step_3.md

@@ -0,0 +1,9 @@
+Add the following environment variable to the `frontend`, `node`, `pumps`,
+and `sensors` services in `docker-compose.yml`.
+
+`DD_ANALYTICS_ENABLED=true`{{copy}}
+
+
+Afterwards restart docker services:
+
+`docker-compose up`{{execute interrupt}}