update changelog

Author: geo-ant

CHANGES.md

@@ -9,7 +9,8 @@ See also here for a [version history](https://crates.io/crates/varpro/versions).
   type.
 * Require `Send` and `Sync` bounds for `BasisFunction` implementors.
 * Expose parrallel calculations for `LevMarProblem` using extra generic
-  arguments and the rayon dependency.
+  arguments and the rayon dependency. Use the `parallel` feature flag
+  to enable.
 * Require `Send` and `Sync` trait bounds on all base functions for building
   separable models whether or not the calculations are to be run in parallel.
   This should not pose restrictions in practice for sane models. If `Send`