adds grafana to docker-compose example

Signed-off-by: Daniel Lee <dan.limerick@gmail.com>

docs/docker-compose.yaml

-version: "2"
+version: "3"
+
+networks:
+  loki:
 
 services:
   loki:
@@ -8,6 +11,8 @@ services:
     volumes:
       - $PWD:/etc/loki
     command: -config.file=/etc/loki/loki-local-config.yaml
+    networks:
+      - loki
 
   promtail:
     image: grafana/promtail:make-images-static-26a87c9
@@ -15,4 +20,15 @@ services:
       - $PWD:/etc/promtail
       - /var/log:/var/log
     command: 
-      -config.file=/etc/promtail/promtail-docker-config.yaml 
+      -config.file=/etc/promtail/promtail-docker-config.yaml
+    networks:
+      - loki
+      
+  grafana:
+    image: grafana/grafana:master
+    ports:
+      - "3000:3000"
+    environment:
+      GF_EXPLORE_ENABLED: "true"
+    networks:
+      - loki