Print message to stderr if result count == --limit

[coxley]

I often find myself doing a search, re-running the search with --count to see if it's the full picture or not, and then running again with an increased --limit.

Automatic paging could be a solution, but GitHub is quick to rate-limit. And much of the time I just want a quick look vs. exhaustive. Letting the user know that there could be more in yellow text is a decent trade-off.