Add a podspec

[elisechant]

Running [email protected] with Cocoapods. Received this CLI message on pod install:

[!] use_native_modules! skipped the react-native dependency 'react-native-autogrow-textinput'. No podspec file was found.
    - Check to see if there is an updated version that contains the necessary podspec file
    - Contact the library maintainers or send them a PR to add a podspec. The react-native-webview podspec is a good example of a package.json driven podspec.
    See https://github.com/react-native-community/react-native-webview/blob/master/react-native-webview.podspec
    - If necessary, you can disable autolinking for the dependency and link it manually. See
    https://github.com/react-native-community/cli/blob/master/docs/autolinking.md#how-can-i-disable-autolinking-for-unsupported-library

[zedtux]

A podspec file has been added 2 months after the opening of this issue, could it be closed ?