doc: add china - google.com warning (#223)

Author: cuttlas

README.md

@@ -185,7 +185,7 @@ type Props = {
 
 `pingTimeout`: amount of time (in ms) that the component should wait for the ping response. Defaults to `10000` ms. If you want to use a different value, it's recommended to use a higher one.
 
-`pingServerUrl`: remote server to ping to. Defaults to `https://www.google.com/` since it's probably one the most stable servers out there, but you can provide your own if needed.
+`pingServerUrl`: remote server to ping to. Defaults to `https://www.google.com/` since it's probably one the most stable servers out there, but you can provide your own if needed. Warning: www.google.com is a blocked domain in China, so if you need your app to be accessible from there, you MUST use another domain.
 
 `shouldPing`: flag that denotes whether the extra ping check will be performed or not. Defaults to `true`.