Missing exceptions warnings in Str documentation

[anon72795300]

https://discuss.ocaml.org/t/publishing-without-github/3232/8:

@anon72795300

I have deleted my account many months ago. Ultimately this is not just for me, but for others too. Contributing should not depend on a single company and compelling community members to join them. I think we all know that is not technically required and we can do better than this.