add comment to explain the MapToCurve algo we use (#225)

crypto/bn254/utils.go

@@ -28,9 +28,11 @@ func VerifySig(sig *bn254.G1Affine, pubkey *bn254.G2Affine, msgBytes [32]byte) (
 
 }
 
-// TODO: which algorithm is this implementing?
-//
-//	add details...
+// MapToCurve implements the simple hash-and-check (also sometimes try-and-increment) algorithm
+// see https://hackmd.io/@benjaminion/bls12-381#Hash-and-check
+// Note that this function needs to be the same as the one used in the contract:
+//     https://github.com/Layr-Labs/eigenlayer-middleware/blob/1feb6ae7e12f33ce8eefb361edb69ee26c118b5d/src/libraries/BN254.sol#L292
+// we don't use the newer constant time hash-to-curve algorithms as they are gas-expensive to compute onchain
 func MapToCurve(digest [32]byte) *bn254.G1Affine {
 
 	one := new(big.Int).SetUint64(1)