Test SMS userId requirement

Adding userId requirement for test profiles used in SMS tests

Author: estgc

src/engage/content/sms/template.md

@@ -31,7 +31,7 @@ Send a test SMS message before you include it as a step in your Journey.
 
 1. After you build your SMS template, click **Test SMS**.
 2. Enter recipient phone numbers for the test message.
-3. Select a profile to test the SMS with and click  **Use as Test Profile**. To ensure merge tags work as expected, use test profiles with traits that apply to your campaign.
+3. Select a profile to test the SMS with and click  **Use as Test Profile**. To ensure merge tags work as expected, use test profiles with traits that apply to your campaign. The selected profile must have a userId assigned to it.
 4. Click **Send Test SMS**.
 
 If a recipient replies "Stop" to the test SMS, Twilio unsubscribes their phone number and sends an opt-out confirmation.