docs(all): Update expo-build-properties instructions

Author: thatzacdavis

docs/index.md

@@ -135,7 +135,18 @@ To use Static Frameworks on iOS, you also need to manually enable this for the p
 $RNFirebaseAsStaticFramework = true
 ```
 
-Expo users may use [expo-build-properties](https://docs.expo.dev/versions/v45.0.0/sdk/build-properties/#pluginconfigtypeios) to turn on `use_frameworks`. We are unsure how Expo users add variables to a Podfile and may need a community contribution to the config-plugin here to do so, PRs welcome!
+Expo users may use [expo-build-properties](https://docs.expo.dev/versions/v45.0.0/sdk/build-properties/#pluginconfigtypeios) to turn on `use_frameworks` by adding the following entry to their `plugins` array in `app.json`:
+
+```json
+[
+  "expo-build-properties",
+  {
+    "ios": {
+      "useFrameworks": "static"
+    }
+  }
+]
+```
 
 > Note `use_frameworks` [is _not_ compatible with Flipper, Hermes, React Native New Architecture or react-native 0.69.0](https://github.com/reactwg/react-native-releases/discussions/21#discussioncomment-2924919). There is already [a patch-package patch available for 0.69.0](https://github.com/mikehardy/rnfbdemo/blob/main/patches/react-native%2B0.69.0.patch) that makes it work with and without Hermes and it will be released with 0.69.1. Community support to help fix `use_frameworks` support for Hermes and New Architecture is welcome!