Add proper documentation

[danmt]

• [x] Document all the code so https://docs.rs/ reads it properly.
• [x] Write a guide on how to set up your local environment to use znap.
• [x] Write an end to end tutorial on working with znap.
• [x] Set up a informational site similar to https://www.anchor-lang.com/

[SergioRibera]

https://github.com/coral-xyz/anchor/tree/master/docs

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