Add a note to the README.md and archive the repo if it is deprecated

[helje5]

So apparently this repo is deprecated. Nothing points at that! So if that is the case I suggest:

• add a BIG note to the README that the repo is dead
• archive it in GitHub, which adds extra warnings (you can do this in the GitHub settings of the repo)

From #18:

As an aside, we encourage you to migrate away from the deprecated C API if possible and to the standard Wasm C API wasmer_wasm.h instead.

[helje5]

The https://github.com/wasmerio/wasmer repo also still refers to this thing, and so does the documentation. Is there documentation for the "new way" of doing things?

[helje5]

To answer myself, it seems to be this: https://github.com/WebAssembly/wasm-c-api