Document runtime architecture

[rigor789]

References:

• https://github.com/NativeScript/NativeScript/wiki/Deep-dive:-How-NativeScript%27s-JS--native-bindings-work

[rigor789]

• https://v7.docs.nativescript.org/core-concepts/technical-overview
• https://v7.docs.nativescript.org/core-concepts/ios-runtime/overview
• https://v7.docs.nativescript.org/core-concepts/android-runtime/overview

From #89

[vallemar]

just as a comment, should this comment be taken into account to include it in the architecture? I mean to include something that explains how it is so easy/difficult/or consistent to include layers in the stack https://dev.to/aleed/comment/23m2h