add mailhog container for local development

{{cookiecutter.project_slug}}/dev.yml

@@ -13,6 +13,13 @@ services:
     environment:
       - POSTGRES_USER={{cookiecutter.project_slug}}
 
+{% if cookiecutter.use_docker == 'y' %}      
+  mailhog:
+    image: mailhog/mailhog
+    ports:
+      - "8025:8025"
+{% endif %}
+
   django:
     build:
       context: .
@@ -28,6 +35,10 @@ services:
       - "8000:8000"
     links:
       - postgres
+{% if cookiecutter.use_docker == 'y' %}
+      - mailhog
+{% endif %}
+
 {% if cookiecutter.use_pycharm == 'y' %}
   pycharm:
     build: