docs: add explanation regarding appcenter token (#5063)

Author: jeremybarbet

src/platforms/react-native/manual-setup/codepush.mdx

@@ -81,4 +81,16 @@ If you don't want to use the automatically computed release format, you will nee
 sentry-cli react-native appcenter {APP} ios ./build/CodePush --deployment {DEPLOYMENT} --dist {DIST} --release-name {RELEASE_NAME}
 ```
 
+<Alert level="info">
+
+Make sure to export the `APPCENTER_ACCESS_TOKEN` in your environment in order to run the `appcenter` commands above. Otherwise you will get the following error:
+
+```bash
+Command 'appcenter codepush deployment history' requires a logged in user. Use the 'appcenter login' command to log in.
+```
+
+You can find more information about this in the [AppCenter CLI](https://docs.microsoft.com/en-us/appcenter/cli/#logging-in) documentation.
+
+</Alert>
+
 If you still have issues with CodePush source maps, you can refer to [Source Maps for Other Platforms](/platforms/react-native/sourcemaps/) to manually bundle and upload source maps to Sentry.