docs: Effective Gno (gnolang#1000)

I'm working towards a concise style, suggesting an initial review of
[Effective Go](https://go.dev/doc/effective_go), followed by
Gno-specific practices. I'm also considering making code snippets in
this documentation unit-testable.

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Signed-off-by: Manfred Touron <[email protected]>
Signed-off-by: moul <[email protected]>
Co-authored-by: jon roethke <[email protected]>
Co-authored-by: Leon Hudak <[email protected]>
Co-authored-by: Morgan <[email protected]>
Co-authored-by: Marc Vertes <[email protected]>