Update README.md

[gmf-uah]

Fixed the 'unpacked extension' link and revised wording for clarity

[google-cla]

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[oliverdunk]

Let us know once you've signed the CLA and we can take a look at this. Thanks!

[gmf-uah]

Hi there,

I signed the CLA a few days ago as of writing. Thank you for the response :) I hope my changes are helpful, even if minor.