Fix old doc reference

src/prng.rs

@@ -3,8 +3,7 @@
 //!
 //! At the moment two prngs are available: [`rand::rngs::StdRng`] and [`crate::random::Random`].
 //! Both of these claim to be cryptographic secure prngs. Provided of course the seeds from `hwrng`
-//! are secure to begin with, which drastically depends on the board used, see remarks in [`crate::hwrng`] module!
-
+//! are secure to begin with, which drastically depends on the board used, see remarks in [RIOTs documentation](https://doc.riot-os.org/group__drivers__periph__hwrng.html).
 
 use embedded_hal::prelude::_embedded_hal_blocking_rng_Read;
 use rand::{rngs::StdRng, SeedableRng};