add note on `--dev` behavior (#9953)

* add note on `--dev` behavior

* Update client/cli/src/params/shared_params.rs

* Update client/cli/src/params/shared_params.rs

* clippy fmt

* Update client/cli/src/params/shared_params.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Update client/cli/src/params/shared_params.rs

Co-authored-by: adoerr <0xad@gmx.net>
Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>