docs(v4): add migration guide (#4110)
docs(v4): add migration guide (#4110)

* docs(v4): add migration guide

This is a temporary location, but will allow us to link towards it until it's in the main documentation.

* add example for routing

* mention bundle size difference of helper

* fix grammar?

Co-Authored-By: Youcef Mammar <9deb3f4994af72b1748001b4fb135d508f646db2@users.noreply.github.com>

* add example for history change

algolia/instantsearch.js,algolia/instantsearch.js,algolia/instantsearch.js