message: doc(readme) Add more indexes to more documentations.
diff: Wasmer provides multiple documentations. Here are some pointers:
  -* [The public documentation](https://docs.wasmer.io/),
  -* [The Rust crates documentation](https://wasmerio.github.io/wasmer/),
  -* [The collection of examples](https://github.com/wasmerio/wasmer/blob/master/examples/README.md),
  -* [Documentations for all embeddings/language integrations](https://github.com/wasmerio/wasmer/blob/master/README.md).
  +* [The Wasmer runtime
  + `README.md`](https://github.com/wasmerio/wasmer/blob/master/README.md)
  + is a good start for the first steps, like installations, first runs etc.,
  +* [The public documentation](https://docs.wasmer.io/) contains all the
  + documentation you need to learn about Wasmer and WebAssembly,
  +* [The Rust crates documentations](https://wasmerio.github.io/wasmer/)
  + contain all the documentations to use the `wasmer-*` Rust crates,
  + with many examples,
  +* [The collection of
  + examples](https://github.com/wasmerio/wasmer/blob/master/examples/README.md)
  + illustrates how to use Wasmer and its numerous features through very
  + commented examples,
  +* [Documentations for all embeddings/language
  + integrations](https://github.com/wasmerio/wasmer/blob/master/README.md):
  + the Wasmer runtime can be embeddeded in various languages or
  + environments, each embedding provides its own documentation, book
  + etc.,
  +* [OS distro packaging
  + notes](https://github.com/wasmerio/wasmer/blob/master/PACKAGING.md)
  + contains notes about how to package Wasmer for OS distributions.
  