Add settings for postgres

sample.env

@@ -79,7 +79,7 @@ LDAP_PASSWORD=
 ALLOW_GREENLIGHT_ACCOUNTS=true
 
 # To enable reCaptcha on the user sign up, define these 2 keys
-# You can obtain these keys by registering your domain using the following url: 
+# You can obtain these keys by registering your domain using the following url:
 #
 #  https://www.google.com/recaptcha/admin
 #
@@ -176,3 +176,12 @@ ENABLE_GOOGLE_CALENDAR_BUTTON=
 # Force SSL
 #
 # ENABLE_SSL=true
+
+# Database settings
+# Greenlight works out of the box with sqlite3, but if postgresql is required, especially for production
+# These variables should also be included.
+# DB_ADAPTER=postgresql
+# DB_HOST=postgres.example.com
+# DB_NAME=greenlight_production
+# DB_USERNAME=postgres
+# DB_PASSWORD=password