Add 1.21 to README.md

Author: rom1504

docs/README.md

@@ -11,7 +11,7 @@ flying-squid
 Create Minecraft servers with a powerful, stable, and high level JavaScript API.
 
 ## Features
-* Support for Minecraft 1.8, 1.9, 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20
+* Support for Minecraft 1.8, 1.9, 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20, 1.21
 * Players can see the world
 * Players see each other in-game and in tab
 * Digging