Improved docs, adding repo structure and libraries README

lib/README.md

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+# Wasmer Libraries
+
+Wasmer is modularized into different libraries, separated into three main sections:
+* [Runtime](#Runtime)
+* [Integrations](#Integrations)
+* [Backends](#Backends)
+
+## Runtime
+
+The core of Wasmer is the runtime.
+It provides the necessary abstractions on top of the WebAssembly specification.
+
+We separated the runtime into two main libraries:
+* [runtime-core](./runtime-core/): The main implementation of the runtime
+* [runtime](./runtime/): Easy-to-use wrappers on top of runtime-core
+
+## Integrations
+
+The integrations are separated implementations in top of our runtime, that let Wasmer run more WebAssembly files.
+
+Wasmer intends to support different integrations:
+* [emscripten](./emscripten): it let us run emscripten-generated WebAssembly files, such as lua or Nginx.
+* Go ABI: _we will work on this soon! Would you like to help us? 💪_
+* Blazor: _researching period, see [tracking issue](https://github.com/wasmerio/wasmer/issues/97)_
+
+
+## Backends
+
+The backends let Wasmer generate code from WebAssembly files, in a way that is abstracted from the 
+IR library itself.
+
+* [clif-backend](./clif-backend/): The integration of Wasmer with Cranelift