Chocolatey pkg for windows.

[Spunkie]

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I've made a guetzli chocolatey package that has just gotten through moderation. So for windows people running chocolatey, getting access to guetzli is as simple as running choco install guetzli now. The pkg should automatically choose the appropriate x86/x64 exe and create PATH shims so it's accessible system wide as guetzli

Also there is an appveyor build that runs twice a day to checks for new versions. So within a day of a new github release here there should be an updated pkg automatically submitted to chocolatey.

Normally I would submit a PR to add this information in the README.md next the the likes of apt/yum/brew/etc but guetzli doesn't really have an installation section. Where would be the best place to put this information? Should I add an installation section or just stick this information in the middle of the using section?