It's not clear to me if Vuex 3 and Vue 2 are supported by vuex-persistedstate 4

[jsekulowicz]

• vuex-persistedstate version: 3.2.0

What you did:
I wanted to upgrade from 3.2.0 to 4.1.0 and checked out the changelog.

What happened:
I was not sure whether vuex-persistedstate 4 supports Vuex 3 and Vue 2 anymore. When I upgraded it seemed to work, but it's possible that something will break.

Problem description:
I can't tell if the older Vuex / Vue versions are supported, especially because in this commit the usage example for Vuex 3 has been removed and the For usage with for Vuex 3 and Vue 2, please see [3.x.x branch](https://github.com/robinvdvleuten/vuex-persistedstate/tree/3.x.x). note has been added.

I couldn't find the explicit information about Vuex 3 and Vue 2 not being supported though.

Suggested solution:
Bring back the information about the usage with Vuex 3 / Vue 2 or add an explicit note that these versions are supported/not supported along with Vuex 4 / Vue 3.