There’s some messaging on the Quality Profile list, but no notifications and no good way to automate this (unless you’re really into scripting, I guess).
If you want to see what new rules have been added in the default profile that aren’t in your custom profile, you can do a profile comparison (under the cog menu in the list of profiles).
To add new rules:
Go to the Sonar way profile page
Click on the active rule count to get the list of rules in the profile
Bulk Change-> Activate in… → [pick your profile]
The rules that aren’t already in your profile will be added. You could then use the audit trail on the custom profile to see what got added.