Objective-C Bridging Header Instructions

[andreyguenov]

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Instructions for how to make an Objective-C Bridging header in the README.md file to make it easier to implement the SDK for beginners.

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[andreyguenov]

I signed it!

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[sstepashka]

Why you use Swift library in ObjC? We have ObjC library for that. https://github.com/api-ai/apiai-ios-client