`Irmin_watcher.v`

[panglesd]

It is not clear how to use Irmin_watcher.v:

• It's type is Core.t, which is not exposed in the toplevel Irmin_watcher module and so ends up in a hidden module (Irmin_watcher__.Core) and thus not in the documentation.
• The documentation says to use v id p f but the type is abstract...