docs: mention code suggestions status bar item in readme
Description
This is a follow-up from our internal conversation https://gitlab.slack.com/archives/C013QJ9NEPL/p1710944656020629?thread_ts=1710942372.631249&cid=C013QJ9NEPL
The status bar item is a good source of information about why code suggestions might not work. But it might not be obvious to users that the icon exists.