If I open a PR and am looking at it, I'd like some indication that a change was made to the PR I'm looking it rather than having to refresh the page or check email.

For example, either a notification could pop-up in the right corner of the browser that something changed and the page needs refresh, or the page could just automatically update to show changes that are happening in near real-time.

It is annoying to IM someone asking them to review the PR because they were busy and find out that some time before they had approved the PR and I was looking at stale data in the PR page I had open in front of me.