Update security_groups.md (#4219)

Author: mtulio

docs/deploy/security_groups.md

@@ -43,6 +43,7 @@ Note that while you can turn off the shared backend security group feature by se
 **Specification:** Use `--backend-security-group` to pass in a security group ID to use as a custom shared backend security group. 
 
 **Important Notes:**
+
 * The Custom Shared Backend Security Group (`--backend-security-group` option) only works when the automatic addition of Inbound Rules to the Node/ENI Security Group is enabled.
 * If a Custom Frontend Security Group is configured, you must set the annotation `service.beta.kubernetes.io/aws-load-balancer-manage-backend-security-group-rules: "true"` for the Custom Shared Backend Security Group to work correctly.