Update index.md (#6406)

Missing command 
/usr/share/opensearch/bin/opensearch-keystore add

Signed-off-by: pawelw1 <[email protected]>

Author: pawelw1

_observing-your-data/notifications/index.md

@@ -123,8 +123,8 @@ To send or receive notifications with email, choose **Email** as the channel typ
 If your email provider requires SSL or TLS, you must authenticate each sender account before you can send an email. Enter the sender account credentials in the OpenSearch keystore using the command line interface (CLI). Run the following commands (in your OpenSearch directory) to enter your user name and password. The <sender_name> is the name you entered for **Sender** earlier.
 
 ```json
-opensearch.notifications.core.email.<sender_name>.username
-opensearch.notifications.core.email.<sender_name>.password
+/usr/share/opensearch/bin/opensearch-keystore add opensearch.notifications.core.email.<sender_name>.username
+/usr/share/opensearch/bin/opensearch-keystore add opensearch.notifications.core.email.<sender_name>.password
 ```
 
 To change or update your credentials (after you’ve added them to the keystore on every node), call the reload API to automatically update those credentials without restarting OpenSearch.