docs(examples): reorganize examples and tutorials, add an index

TODO

-- pull mdns out as its own separate package
+- [ ] pull mdns out as its own separate package

examples/README.md

+# `go-libp2p` examples and tutorials
+
+In this folder, you can find a variety of examples to help you get started in using go-libp2p. Every example as a specific purpose and some of each incorporate a full tutorial that you can follow through, helping you expand your knowledge about libp2p and p2p networks in general.
+
+Let us know if you find any issue or if you want to contribute and add a new tutorial, feel welcome to submit a pr, thank you!
+
+## Examples and Tutorials
+
+- [The libp2p 'host'](./libp2p-host)
+- [Building an http proxy with libp2p](./http-proxy)
+- [Protocol Multiplexing with multicodecs](./protocol-multiplexing-with-multicodecs)
+- [An echo host](./echo)

tutorial/001-the-host/README.md → examples/libp2p-host/README.md

 # The libp2p 'host'
+
 For most applications, the host is the basic building block you'll need to get
 started. This guide will show how to construct and use a simple host.
 The host is an abstraction that manages services on top of a swarm. It provides