Add SPF description

[MAILPOET-2693]

assets/js/src/settings/pages/send_with/other/other_sending_methods.tsx

@@ -1,10 +1,13 @@
 import React from 'react';
 import SendingMethod from './sending_method';
+import SPF from './spf';
 
 export default function OtherSendingMethods() {
   return (
     <div className="mailpoet-settings-grid">
       <SendingMethod />
+
+      <SPF />
     </div>
   );
 }

assets/js/src/settings/pages/send_with/other/spf.tsx

@@ -0,0 +1,14 @@
+import React from 'react';
+import { t } from 'common/functions';
+import { Label, Inputs } from 'settings/components';
+
+export default function SPF() {
+  return (
+    <>
+      <Label title={t('spfTitle')} description={t('spfDescription')} htmlFor="" />
+      <Inputs>
+        {t('spfSetup')}
+      </Inputs>
+    </>
+  );
+}