update README with info about using this component in NextJs

[pietrop]

Is your feature request related to a problem? Please describe.

update README with info about using in NextJs
Describe the solution you'd like

Add this to README

Next.js is a serverside renderer which conflicts with the component.
You can import it like this

const SlateTranscriptEditor = dynamic(import('slate-transcript-editor'), { ssr: false }) 

Describe alternatives you've considered

NA
Additional context

NA