docs: SimpleSmt::compute_mutations note

src/merkle/smt/simple/mod.rs

@@ -218,6 +218,10 @@ impl<const DEPTH: u8> SimpleSmt<DEPTH> {
     /// [`SimpleSmt::apply_mutations()`] can be called in order to commit these changes to the
     /// Merkle tree, or [`drop()`] to discard them.
     ///
+    /// **Note:** Parallel computation is only supported for trees whose depth is a multiple of 8.
+    /// Since `SimpleSmt` can have a depth that isn't a multiple of 8, this method defaults to the
+    /// sequential implementation to ensure correctness.
+    ///
     /// # Example
     /// ```
     /// # use miden_crypto::{hash::rpo::RpoDigest, Felt, Word};