Document minimum Android SDK version and iOS build target

[Will Madden]

Is your feature request related to a problem? Please describe.

The plugin fails to build on Android unless:

• compileSdkVersion >= 32
• minSdkVersion >= 22
• targetSdkVersion >= 32

and fails to build on iOS unless:

• minimum deployment target >= 13.0 (which needs to be set in the Podfile and XCode config)

Describe the solution you'd like

It would be really helpful if this was documented in the README.

[jcesarmobile]

Those are really Capacitor 4 requirements, but the readme should mention that the plugin should be used with Capacitor 4 only.