Clarify algorithm complexity in changelog

Updated the description of the Term * Term speedup to specify the use of an O(n) sort algorithm instead of Python's O(log(n)) sorted function.

Author: Zeroto521

CHANGELOG.md

@@ -23,7 +23,7 @@
 - Speed up MatrixExpr.add.reduce via quicksum
 - Speed up np.ndarray(..., dtype=np.float64) @ MatrixExpr
 - Speed up Expr * Expr via C-level API and Term * Term
-- Speed up Term * Term via $O(n)$ algorithm instead of Python sorted function. `Term.__mul__` requires that Term.vartuple is sorted.
+- Speed up Term * Term via a $O(n)$ sort algorithm instead of Python $O(\log(n))$ sorted function. `Term.__mul__` requires that Term.vartuple is sorted.
 - Rename from `Term.__add__` to `Term.__mul__`, due to this method only works with Expr * Expr.
 - MatrixExpr and MatrixExprCons use `__array_ufunc__` protocol to control all numpy.ufunc inputs and outputs
 - Set `__array_priority__` for MatrixExpr and MatrixExprCons