docs: Effective Gno (#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 <94029+moul@users.noreply.github.com>
Signed-off-by: moul <94029+moul@users.noreply.github.com>
Co-authored-by: jon roethke <waymobetta@users.noreply.github.com>
Co-authored-by: Leon Hudak <33522493+leohhhn@users.noreply.github.com>
Co-authored-by: Morgan <git@howl.moe>
Co-authored-by: Marc Vertes <mvertes@free.fr>