Proptype warning on search input

[peterbe]

Warning: Failed prop type: You provided a `value` prop to a form field without an `onChange` handler. This will render a read-only field. If the field should be mutable use `defaultValue`. Otherwise, set either `onChange` or `readOnly`.
    in input (created by SearchBox)
    in form (created by SearchBox)
    in div (created by SearchBox)
    in SearchBox (at App.js:227)
    in div
    in div
    in Unknown (at App.js:226)
    in div
    in Unknown (at App.js:225)
    in SearchkitProvider (at App.js:224)
    in div (at App.js:223)
    in App (at src/index.js:10)

[peterbe]

It's a "bug" in SearchKit. Perhaps addressing #417 is the right thing to do.