added support to override backend values on a per certificate basis

README.md

@@ -56,6 +56,12 @@ san: []
 
 # services to restart if this certificate changes
 depending_services: []
+
+# which backend to use, can be 'selfsigned' or 'letsencrypt'
+backend: 'selfsigned'
+
+# overwrite a backend setting for this certificate
+backend_override: {}
 ```
 
 ### Backends