docs: v3.6.0 changelog

Author: kozistr

docs/changelogs/v3.6.0.md

@@ -12,6 +12,7 @@
     * will raise `NoComplexParameterError` for unsupported optimizers, due to its design or not-yet-implemented.
 * Support `maximize` parameter. (#370, #380)
     * `maximize`: maximize the objective with respect to the params, instead of minimizing.
+* Implement `copy_stochastic()` method. (#381)
 
 ### Update