Add a basic migration guide

Author: zoontek

MIGRATION.md

@@ -0,0 +1,39 @@
+# Migration from v2
+
+## What's new
+
+- Windows support ([#530](https://github.com/zoontek/react-native-permissions/pull/530))
+- Android 11 support
+- iOS 9 support dropped
+- A new iOS permission handler: `Permission-LocationAccuracy` ([#503](https://github.com/zoontek/react-native-permissions/pull/503))
+- A new iOS permission handler: `Permission-PhotoLibraryAddOnly` ([#510](https://github.com/zoontek/react-native-permissions/pull/510))
+- New methods for iOS14+: `checkLocationAccuracy`, `requestLocationAccuracy`, `openLimitedPhotoLibraryPicker` ([#503](https://github.com/zoontek/react-native-permissions/pull/503), [#510](https://github.com/zoontek/react-native-permissions/pull/510))
+- Support of the new `Limited` status for `PhotoLibrary` permission ([#510](https://github.com/zoontek/react-native-permissions/pull/510))
+- Support of the new `Limited` status for `Notifications` permission (=`Ephemeral`, (see [Apple doc](https://developer.apple.com/documentation/usernotifications/unauthorizationstatus/unauthorizationstatusephemeral?language=objc))
+
+## Code modifications
+
+1. `.podspec` extension is no longer required in your `Podfile`:
+
+```diff
+target 'YourAwesomeProject' do
+
+  # …
+
+  permissions_path = '../node_modules/react-native-permissions/ios'
+
+- pod 'Permission-Calendars', :path => "#{permissions_path}/Calendars.podspec"
++ pod 'Permission-Calendars', :path => "#{permissions_path}/Calendars"
+- pod 'Permission-Camera', :path => "#{permissions_path}/Camera.podspec"
++ pod 'Permission-Camera', :path => "#{permissions_path}/Camera"
+
+  # …
+
+end
+```
+
+2. `request(PERMISSIONS.IOS.PHOTO_LIBRARY)` and `requestNotifications` could now resolve with a `RESULTS.LIMITED` permission status.
+
+## Known issues
+
+Updating the permission status to `Ask me next time` in your app settings will not work on Android 11.