chore: improve BLS constant documentation (paradigmxyz#5976)

crates/rpc/rpc-types/src/beacon/constants.rs

@@ -1,4 +1,17 @@
-pub const BLS_DST: &[u8] = b"BLS_SIG_BLS12381G2_XMD:SHA-256_SSWU_RO_POP_";
+/// The Domain Separation Tag for hash_to_point in Ethereum beacon chain BLS12-381 signatures.
+///
+/// This is also the name of the ciphersuite that defines beacon chain BLS signatures.
+///
+/// See:
+/// <https://github.com/ethereum/consensus-specs/blob/ffa95b7b72149960c5aded5c95fb40d64bcab199/specs/phase0/beacon-chain.md#bls-signatures>
+/// <https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-bls-signature-04>
+pub const BLS_DST_SIG: &[u8] = b"BLS_SIG_BLS12381G2_XMD:SHA-256_SSWU_RO_POP_";
+
+/// The number of bytes in a BLS12-381 public key.
 pub const BLS_PUBLIC_KEY_BYTES_LEN: usize = 48;
+
+/// The number of bytes in a BLS12-381 secret key.
 pub const BLS_SECRET_KEY_BYTES_LEN: usize = 32;
+
+/// The number of bytes in a BLS12-381 signature.
 pub const BLS_SIGNATURE_BYTES_LEN: usize = 96;