docs: update readme for drive readme

[sbatson5]

What's in this PR?

I was going through the example for google drive and came across the README, where I was told to create oauth2.keys.json. What wasn't immediately clear was that everything needed to be nested under a key of web, as shown here. A specific example would have been really helpful, so I added a quick one.

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[sbatson5]

@googlebot I signed it!

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[JustinBeckwith]

This is lovely! Thank you!

[bcoe]

@sbatson5 thanks for the contribution 👌 this will be merged as soon as tests pass.