Improve documentation to describe more example use cases

[CJ42]

I'm submitting a...

• bug report
• feature request
• question about the decisions made in the repository
• question about how to use this project

Summary

So far the documentation of erc725.js mainly focuses on the API, and how to use the functions.

However, it does not provide on how the library could be used for generic and common use cases. For instance:

• retrieving the list of issued or received assets
• retrieving the list of controllers (LSP6)
• retrieving an entry in a specific array index
• encoding Verifiable URI (for Universal Profiles or Digital Assets)
• retrieving the JSON metadata (for a Universal Profile or Digital Asset)
• creating a schema to store and encode a list of entries (e.g: MusicPlaylist[])

Other information (e.g. detailed explanation, stack traces, related issues, suggestions how to fix, links for us to have context, eg. StackOverflow, personal fork, etc.)

A comprehensive list of good ideas of how the library could be used + the common use cases should be created to know what these new documentation pages should contain.