Add a description for slack channel form field (#25353)

frontend/src/metabase/admin/settings/slack/components/SlackStatusForm/SlackStatusForm.tsx

 import React, { useCallback, useMemo } from "react";
+import { t } from "ttag";
 import Form from "metabase/containers/FormikForm";
 import { SlackSettings } from "metabase-types/api";
 import { getSlackForm } from "../../forms";
@@ -21,7 +22,10 @@ const SlackStatusForm = ({ settings }: SlackStatusFormProps): JSX.Element => {
       {({ Form, FormField }: FormProps) => (
         <Form>
           <FormField name="slack-app-token" />
-          <FormField name="slack-files-channel" />
+          <FormField
+            name="slack-files-channel"
+            description={t`We'll upload charts and tables here before sending out dashboard subscriptions.`}
+          />
         </Form>
       )}
     </Form>

frontend/src/metabase/admin/settings/slack/components/SlackStatusForm/types.ts

@@ -7,4 +7,5 @@ export interface FormProps {
 
 export interface FormFieldProps {
   name: string;
+  description?: string;
 }