Add missing trait "use" in doc tests

Change-Id: I27d64f8f1654ed0399c09c48b9c41e84aac1aa3a
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/69047
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
diff --git a/rust/bssl-crypto/src/digest.rs b/rust/bssl-crypto/src/digest.rs
index 59d3b2a..d3d74c0 100644
--- a/rust/bssl-crypto/src/digest.rs
+++ b/rust/bssl-crypto/src/digest.rs
@@ -16,7 +16,7 @@
 //! Hash functions.
 //!
 //! ```
-//! use bssl_crypto::digest;
+//! use bssl_crypto::digest::{self, Algorithm, WithOutputLength};
 //!
 //! // One-shot hashing.
 //! let digest: [u8; 32] = digest::Sha256::hash(b"hello");