doc: Document batch insertion error (#75)

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---------

Co-authored-by: Vivian Plasencia <[email protected]>

Author: Ben-PH

crates/lean-imt/src/hashed_tree.rs

@@ -40,6 +40,10 @@ where
     }
 
     /// Inserts multiple leaves.
+    ///
+    /// # Errors
+    ///
+    /// Will return [`LeanIMTError::EmptyBatchInsert`] if `leaves` is an empty array
     pub fn insert_many(&mut self, leaves: &[[u8; N]]) -> Result<(), LeanIMTError> {
         self.tree.insert_many(leaves, H::hash)
     }

crates/lean-imt/src/lean_imt.rs

@@ -86,6 +86,10 @@ impl<const N: usize> LeanIMT<N> {
     }
 
     /// Inserts multiple leaves.
+    ///
+    /// # Errors
+    ///
+    /// Will return [`LeanIMTError::EmptyBatchInsert`] if `leaves` is an empty array
     pub fn insert_many(
         &mut self,
         leaves: &[[u8; N]],