Update plain_rules.md

Author: AlvaroVega

docs/API/plain_rules.md

@@ -372,9 +372,10 @@ The `template`, `from`, `to` and `subject` fields perform [string substitution](
 content body resulting in `template` is an HTML content then email will be sent as HTML and plain text, in order to
 ensure accesibility and compability.
 
-Regarding with `to` field, it is possible to include several email destinataries by separating with `;` like:
+Regarding with `to` field, it is possible to include several email destinataries by separating with `;` or even better `, ` like:
 ```json
-            "to": "someone@acme.com; anotherone@acme.com",
+            "to": "someone@acme.com; anotherone@acme.com"
+            "to": "someone@acme.com, anotherone@acme.com"
 ```
 
 Additionally, Email action could include a `smtp` field to include SMTP configuration (see