Add information to save the Sandbox toggle on settings before authenticate

Add information in the faq on "How do I enable a sandbox instance?", to save the settings, then authenticate.

Change from:
"To send data to a Salesforce sandbox instance, navigate to Settings > Advanced Settings, toggle on the “Sandbox Instance” setting, and authenticate."

To:
"To send data to a Salesforce sandbox instance, navigate to Settings > Advanced Settings, toggle on the "Sandbox Instance" setting, save the setting and then authenticate. “

Author: tanjinhong72

src/connections/destinations/catalog/actions-salesforce/index.md

@@ -116,7 +116,7 @@ Review the tables below to see how settings from Salesforce (Classic) were migra
 ## FAQ
 
 ### How do I enable a sandbox instance?
-To send data to a Salesforce sandbox instance, navigate to **Settings > Advanced Settings**, toggle on the "Sandbox Instance" setting, and authenticate. If you are already authenticated, please disconnect and reconnect with your sandbox username. 
+To send data to a Salesforce sandbox instance, navigate to **Settings > Advanced Settings**, toggle on the "Sandbox Instance" setting, save the setting and then authenticate. If you are already authenticated, please disconnect and reconnect with your sandbox username. 
 
 Your Salesforce sandbox username appends the sandbox name to your Salesforce production username. For example, if a username for a production org is `[email protected]` and the sandbox is named `test`, the username to log in to the sandbox is `[email protected]`.