[docs] Add React Native 0.81 to compatibility table (#4007)

## Description

We set minimal version for Gesture Handler 3 to 0.82, but Expo SDK was
still on RN 0.81. I've checked whether Gesture Handler build on RN 0.81
and added it to compatibility table to avoid multiple questions about
support.

## Test plan

Check docs.

Verified on standalone apps that both versions work.

Author: m-bert

packages/react-native-gesture-handler/compatibility.json

@@ -1,8 +1,8 @@
 {
   "3.0.0-beta.2": {
-    "react-native": ["0.82", "0.83", "0.84"]
+    "react-native": ["0.81", "0.82", "0.83", "0.84"]
   },
   "3.0.0-beta.1": {
-    "react-native": ["0.82", "0.83", "0.84"]
+    "react-native": ["0.81", "0.82", "0.83", "0.84"]
   }
 }