docs: Add Cargo.toml style guide (#535)

* first draft

* Add exampls

* Change negative example

* Change order of good and bad examples

* typos

* review fix

* Update modules/contributor/pages/code-style-guide.adoc

Co-authored-by: Techassi <git@techassi.dev>

* changed some wording

* removed 'we'

* Update modules/contributor/pages/code-style-guide.adoc

Co-authored-by: Techassi <git@techassi.dev>

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Co-authored-by: Techassi <git@techassi.dev>

Author: fhennig