docs: document end exclusive to compute subtree root

nmt.go

@@ -646,6 +646,7 @@ func (n *NamespacedMerkleTree) updateMinMaxID(id namespace.ID) {
 
 // ComputeSubtreeRoot takes a leaf range and returns the corresponding subtree root.
 // Also, it requires the start and end range to correctly reference an inner node.
+// The provided range, defined by start and end, is end-exclusive.
 func (n *NamespacedMerkleTree) ComputeSubtreeRoot(start, end int) ([]byte, error) {
 	if start < 0 {
 		return nil, fmt.Errorf("start %d shouldn't be strictly negative", start)

proof.go

@@ -506,7 +506,7 @@ func (proof Proof) VerifySubtreeRootInclusion(nth *NmtHasher, subtreeRoots [][]b
 	// check whether the number of ranges matches the number of subtree roots.
 	// if not, make an early return.
 	if len(subtreeRoots) != len(ranges) {
-		return false, fmt.Errorf("number of subtree roots %d is different than the number of leaf ranges %d", len(subtreeRoots), len(ranges))
+		return false, fmt.Errorf("number of subtree roots %d is different than the number of the expected leaf ranges %d", len(subtreeRoots), len(ranges))
 	}
 
 	var computeRoot func(start, end int) ([]byte, error)