Reword part of the Implementation Considerations

draft-lucas-bkdf.md

@@ -357,7 +357,7 @@ There are several ways to optimise the pseudocode, which is written for readabil
 - Instead of `x % spaceCost`, one can do `x & (spaceCost - 1)` because `spaceCost` is a power of 2.
 - Skip the XORing of outputs when `parallelism = 1`.
 - Instead of `Ceiling(length / HASH_LEN)`, one can do `(length + HASH_LEN - 1) / HASH_LEN`.
-- Convert the key derivation domain separation string to bytes once rather than in each iteration of the loop.
+- Convert constants/unchanging values to bytes once rather than in each loop iteration or in multiple loops.
 - Use an incremental hash function API rather than manual concatenation.
 - If possible with the hash function API, cache the hash function state after processing the key so it does not need to be processed again.