Add steps for encoding and decoding

[ben221199]

This pull request adds steps to tell in a basic way how to encode and decode multiaddrs.

[ben221199]

I understand your view about the pseudo-code. However, I think that it better to have some neutral pseudo-code instead of pointing developers coding in some language to an implementation in another language. I even think that the implementations in this GitHub organization shouldn't even be part of the specifications and just keep it only core level, but that is my point of view.