message: add intented use of the api
diff: @@ -8,10 +8,15 @@ use crate::{Entry, EntryLink, NodeData, Error, EntryKind};
  /// With only some of the leaves/nodes pre-loaded / pre-generated.
  /// Exact amount of the loaded data can be calculated by the constructing party,
  /// depending on the length of the tree and maximum amount of operations that are going
  -/// to happen after construction.
  +/// to happen after construction. `Tree` should not be used as self-contained data structure,
  +/// since it's internal state can grow indefinitely after serial operations.
  +/// Intended use of this `Tree` is to instantiate it based on partially loaded data (see example
  +/// how to pick right nodes from the array representation of MMR Tree), perform several operations
  +/// (append-s/delete-s) and then drop it.
  pub struct Tree {
  stored: HashMap<u32, Entry>,
  + // This can grow indefinitely if `Tree` is misused as a self-contained data structure
  generated: Vec<Entry>,
  // number of persistent(!) tree entries
  