Update Readme for Android permission handling

[radioactiveman]

According to the code and compiler warnings, using OnRequestPermissionsResult() from the Android Permission Handler is deprecated. The Readme still suggests to use this though. Please clarify this.

[Lydecker]

Yup -documentation is well out of date for v3 of this plugin.

As long as you have Essentials 1.5.x - there is no need for anything extra in the OnRequestPermissionsResult() on android from our findings...

[knocte]

The Readme still suggests to use this though.

Can you open a PullRequest please?

[radioactiveman]

Can you open a PullRequest please?

Sure, see #950.