Improve documentation for handling removal of microphone access on iOS.

[Zurigan]

To which pages does your suggestion apply?

https://pub.dev/packages/audio_session#ios-setup

Quote the sentences(s) from the documentation to be improved (if any)

To do so, edit your ios/Podfile as follows:

Describe your suggestion

Update to "To do so, edit your ios/Podfile as follows AND THEN RUN POD INSTALL" ... for anyone who might not understand that that is required in order for the edit to make a difference. Not me, other people. Yup.