Add Kotlin Gradle script example to Android README section

[complexspaces]

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This PR adds a documented example of how to use the Android component when your Android app uses Kotlin script files instead of Groovy scripts to handle the Gradle build system. We've now had ~2-3 people ask about this, so I think that justifies giving the information a proper spot instead of linking to a issue comment over and over.

The implementation is based primarily off this older example I posted last year, with a few changes adapted from 1P's current production scripts. I opted to keep it in a collapsed section to avoid making the README any longer to scroll through.

Closes #166.

[djc]

I don't think I have the experience to be able to review this change.

[complexspaces]

That's perfectly ok, thanks for the heads up. I just wanted to at least give the other maintainers a chance to look it over.

Does it sound fine to wait another week or so for Daniel (as the other person who's worked on Android stuff) and after that just proceed with merging this? These are just documentation changes and I'm entirely confident in the Kotlin script itself being correct.