feat(docs): document the merkle proof verifier functions

docs/modules/ROOT/pages/crypto.adoc

@@ -4,4 +4,24 @@ The OpenZeppelin Rust Contracts provide a crate for common cryptographic procedu
 
 == Verifying Merkle Proofs
 
-TODO: Fill this section out.
+Developers can build a Merkle Tree off-chain, which allows for verifying that an element (leaf) is part of a set by using a Merkle Proof. This technique is widely used for creating whitelists (e.g. for airdrops) and other advanced use cases.
+
+TIP: OpenZeppelin Contracts provides a https://github.com/OpenZeppelin/merkle-tree[JavaScript library] for building trees off-chain and generating proofs.
+
+https://docs.rs/crypto/latest/merkle/struct.Verifier.html[`MerkleProof`] provides:
+
+* https://docs.rs/crypto/latest/merkle/struct.Verifier.html#method.verify[`verify`] - can prove that some value is part of a https://en.wikipedia.org/wiki/Merkle_tree[Merkle tree].
+
+* https://docs.rs/crypto/latest/merkle/struct.Verifier.html#method.verify_multi_proof[`verify_multi_proof`] - can prove multiple values are part of a Merkle tree.
+
+[source,rust]
+----
+pub fn verify(&self, proof: Vec<B256>, root: B256, leaf: B256) -> bool {
+    let proof: Vec<[u8; 32]> = proof.into_iter().map(|m| *m).collect();
+    Verifier::<KeccakBuilder>::verify(&proof, *root, *leaf)
+}
+----
+
+Note that these functions use `keccak256` as the hashing algorithm, but our library also provides generic counterparts: https://docs.rs/crypto/latest/merkle/struct.Verifier.html#method.verify_with_builder[`verify_with_builer`] and https://docs.rs/crypto/latest/merkle/struct.Verifier.html#method.verify_multi_proof_with_builder[`verify_multi_proof_with_builder`].
+
+We also provide an adapter https://docs.rs/crypto/latest/hash/index.html[`hash`] module to use your own hashers in conjunction with them that resembles Rust's standard library's API.