Add codesigning issue notice for iOS SDK (#427)

Added a section about codesigning issues for iOS SDK versions 19.5.6 and 19.5.7.

Author: Br1an-Boyle

README.md

@@ -7,6 +7,13 @@
 
 > React Native wrapper to bridge our iOS and Android SDK
 
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+## ⚠️ May 1st Codesigning issue ⚠️ 
+If you are running iOS SDK [v19.5.6](https://github.com/intercom/intercom-ios/releases/tag/19.5.6) or [v19.5.7](https://github.com/intercom/intercom-ios/releases/tag/19.5.7) and are experiecing a codesigning issue, [please follow these steps](https://github.com/intercom/intercom-ios/wiki/Codesigning-Issue) to resolve it.
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 ### 🏠 [Website](https://intercom.com/)
 
 ### 📚 [Developer Docs](https://developers.intercom.com/installing-intercom/docs/intercom-for-react-native)