docs: enhance instruction around required AppDelegate.m changes

[fivecar]

... in case people miss the all-important change needed to enable true background downloading.

[codecov[bot]]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage :thumbsup:

Coverage data is based on head (f0bfb24) compared to base (c17ef47). Patch has no changes to coverable lines.

Additional details and impacted files

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[github-actions[bot]]

:tada: This PR is included in version 3.0.1 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: