Update docs for checkpointTrie db override

src/checkpointTrie.ts

@@ -29,9 +29,8 @@ export class CheckpointTrie extends BaseTrie {
 
   /**
    * Creates a checkpoint that can later be reverted to or committed.
-   * After this is called, no changes to the trie will be permanently saved
-   * until `commit` is called. Calling `db.put` overrides the checkpointing
-   * mechanism and would directly write to db.
+   * After this is called, no changes to the trie will be permanently saved until `commit` is called.
+   * To override the checkpointing mechanism use `_maindb.put` to write directly write to db.
    */
   checkpoint() {
     const wasCheckpoint = this.isCheckpoint