[#133] Haskell <-> Michelson conversion in doc

Description

Problem: Our contract docs mostly use haskell values to define entrypoints and storage types, however, one may want to interact with the contract using plain Michelson values.

Solution: By default include in the contract doc paragraph about values conversions between Haskell and Michelson.

Related issue(s)

Resolves #133 (closed)

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