add doc for memory_optimize, test=develop (#17010)

* add doc for memory_optimize, test=develop

* update doc, test=develop

* doc update, test=develop

paddle/fluid/pybind/pybind.cc

@@ -1347,7 +1347,16 @@ All parameter, weight, gradient are variables in Paddle.
       .def_property(
           "memory_optimize",
           [](const BuildStrategy &self) { return self.memory_optimize_; },
-          [](BuildStrategy &self, bool b) { self.memory_optimize_ = b; })
+          [](BuildStrategy &self, bool b) { self.memory_optimize_ = b; },
+          R"DOC(The type is BOOL, memory opitimize aims to save total memory 
+                consumption, set to True to enable it.
+                
+                Memory Optimize is our experimental feature, some variables 
+                may be reused/removed by optimize strategy. If you need to
+                fetch some variable values when using this feature, please
+                set the persistable property of the variables to True.
+                
+                Default False)DOC")
       .def_property(
           "is_distribution",
           [](const BuildStrategy &self) { return self.is_distribution_; },