docs: update compatibility table with Socket.IO v4

darrachequesne · darrachequesne · commit e2e24ea75dac · 2021-04-26T09:22:05.000+02:00
diff --git a/README.md b/README.md
@@ -21,7 +21,7 @@ See also:
 | -------------- | ---------------- |
 | 0.9.x  | 1.x |
 | 1.x    | 2.x |
-| 2.x    | 3.x |
+| 2.x    | 3.x / 4.x |
 
 ## Documentation
 
