feat!: Address descriptors

[tcliff111]

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Fixes #294 🦕

[wangela]

• Let's update the README "Usage" section with either a demonstration of Geocoding or a pointer to see examples by examining tests.
• Does https://github.com/googlemaps/google-maps-services-go/blob/master/examples/geocoding/cmdline/main.go need to be updated as well?

[tcliff111]

• Let's update the README "Usage" section with either a demonstration of Geocoding or a pointer to see examples by examining tests.
• Does https://github.com/googlemaps/google-maps-services-go/blob/master/examples/geocoding/cmdline/main.go need to be updated as well?

Just updated the README and also updated the main.go file.