[styles] Document the right react-jss version for legacy style modules (

#14237)

A heads up to users who are using incompatible react-jss versions, potentially resulting in errors such as:
Prop `className` did not match.

docs/src/pages/guides/server-rendering/server-rendering.md

@@ -274,3 +274,4 @@ To check version numbers, run `npm list @material-ui/core` in the environment wh
 ```
 
 - You need to make sure that the server and the client share the same `process.env.NODE_ENV` value.
+- The react-jss dependency version should match the ^8.0.0 semantic versioning.