`error_management.md` mentions non-existent `VerboseError`

[stevenengler]

Hi, I'm trying to upgrade to nom 8 and was trying to figure out how to replace some code that uses VerboseError. While looking around, I noticed that the doc/error_management.md document still discusses VerboseError which doesn't exist anymore, so it looks like this documentation should be updated.

[asibahi]

you need to import nom-language as well, as VerboseError moved there. Its API is otherwise unchanged as far as I can tell.