`book`: Drop v0.2.0 note
`defmt` is a highly efficient logging framework that targets resource-constrained devices, like microcontrollers.
-> **NOTE** this hosted version of the `defmt` book corresponds to the *unreleased* `defmt` v0.2.0,
-> which is currently only available as a git dependency. If you are looking for `defmt` v0.1.x's
-> documentation head to <https://defmt.ferrous-systems.com>.
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## Features
- `println!`-like formatting
