Update Ortac/QCheck-STM Readme with found bugs

[n-osborne]

[jmid]

LGTM, great to have a growing list of example findings! :tada:

Two observations:

• This is meant to document to new-comers that the tool is useful in practice. As such, we might consider adding it to the front-page README, where it is more likely to be seen? :thinking:
• It is not an implementation bug, but the Hashtbl.create weirdness https://github.com/ocaml/ocaml/issues/13469 has been acknowledged in https://github.com/ocaml/ocaml/pull/13474#issuecomment-2388687681 agreeing that the documentation should be adjusted.

[n-osborne]

I missed the evolution of the Hashtbl.create issue! Thanks! I'll add it.

Regarding the question in which README to put the list, I was indeed wondering.

My train of thought was that the list is specific to Ortac/QCheck-STM.

But (1) maybe other plugins will find bugs in the future and a unique list may be preferable and (2) even ocaml.org is displaying the root README for ortac-qcheck-stm plugin (I was mistakenly thinking the opposite here).