Add note regarding devtools preventing sleep

[emcniece]

A debugging session today lead me to discover that binding inspection devtools to the app will prevent this plugin and the native device from sleeping.

The plugin works as expected and native devices sleep when devtools are not active.

This PR adds a note to README clarifying this behaviour:

Note that while developing apps using this plugin, the native device will stay awake while debug tools are attached. For Android this includes Android Studio and the Remote Debugging tools via Chrome. For iOS this includes XCode runtime console and Safari Devtools.

When testing apps on native devices, detatch any developer tools to ensure the plugin works as expected.