Extend mail config and help. #1487

.env.example

@@ -54,6 +54,7 @@ COOKIE_DOMAIN=
 COOKIE_SECURE=false
 
 # If you want Firefly III to mail you, update these settings
+# For instructions, see: https://firefly-iii.readthedocs.io/en/latest/installation/mail.html
 MAIL_DRIVER=log
 MAIL_HOST=smtp.mailtrap.io
 MAIL_PORT=2525
@@ -62,6 +63,12 @@ MAIL_USERNAME=null
 MAIL_PASSWORD=null
 MAIL_ENCRYPTION=null
 
+# Other mail drivers:
+MAILGUN_DOMAIN=
+MAILGUN_SECRET=
+MANDRILL_SECRET=
+SPARKPOST_SECRET=
+
 # Firefly III can send you the following messages
 SEND_REGISTRATION_MAIL=true
 SEND_ERROR_MESSAGE=true
@@ -100,3 +107,5 @@ IS_DOCKER=false
 IS_SANDSTORM=false
 BUNQ_USE_SANDBOX=false
 IS_HEROKU=false
+MAILGUN_DOMAIN=
+MAILGUN_SECRET=