README: Add guidance on passing context to yupResolver (useForm context)

[eotkd4791]

Reason for change

Yup typically uses the schema.validate(values, { context }) pattern, which naturally leads users to try yupResolver(schema, { context }).
However, yupResolver in @hookform/resolvers does not recommend using schemaOptions.context (there is a dev warning in the code), and this is not clearly documented in the README. This can increase debugging cost for users.

What’s changed

• Added a short explanation in the Yup section of the README on how to pass context.
• Clarified that context should be provided via useForm({ context }), and that this value is injected into Yup’s validation context at resolver execution time, with an example.
• Briefly mentioned that passing React state/atoms via schemaOptions.context may appear stale or undefined.

Scope of impact

• Documentation-only change (no behavior changes).

References

• Dev warning inside yup resolver:

  resolvers/yup/src/yup.ts

  Line 100 in 2e9bc7c

  "You should not used the yup options context. Please, use the 'useForm' context object instead",

• Related discussion: Document yupResolver context handling in react-hook-form/resolvers #834