add optional connection-string parameter

Author: mayssamm

articles/communication-services/quickstarts/email/includes/send-email-az-cli.md

@@ -76,13 +76,15 @@ After you add the environment variable, run `source ~/.bash_profile` from your c
 
 ```azurecli-interactive
 az communication email send
+	--connection-string "yourConnectionString"
 	--sender "<[email protected]>"
 	--to "<[email protected]>"
 	--subject "Welcome to Azure Communication Services Email" --text "This email message is sent from Azure Communication Services Email using Azure CLI." 
 ```
 
 Make these replacements in the code:
 
+- Replace `<yourConnectionString>` with your connection string.
 - Replace "<[email protected]>" with the email address you would like to send a message to.
 - Replace "<[email protected]>" with the MailFrom address of your verified domain.