RN: lock package versions in README (#122)

Signed-off-by: Kobie Botha <kobie@journeyapps.com>

Author: kobiebotha

packages/powersync-sdk-react-native/README.md

@@ -38,12 +38,12 @@ This SDK requires HTTP streaming in order to function. The following `fetch` pol
 - react-native-polyfill-globals
 - react-native-url-polyfill
 - text-encoding
-- web-streams-polyfill
+- web-streams-polyfill@3.2.1
 
 These are listed as peer dependencies and need to be added to the React Native project
 
 ```bash
-npx expo install react-native-fetch-api react-native-polyfill-globals react-native-url-polyfill text-encoding web-streams-polyfill base-64 react-native-get-random-values
+npx expo install react-native-fetch-api react-native-polyfill-globals react-native-url-polyfill text-encoding web-streams-polyfill@3.2.1 base-64 react-native-get-random-values@1.9.0
 ```
 
 Enable the polyfills in React Native app with