upload dygraph RNNCell doc and paddle.rand doc (#2022)

doc/fluid/api/dygraph/GRUCell.rst

+..  THIS FILE IS GENERATED BY `gen_doc.{py|sh}`
+    !DO NOT EDIT THIS FILE MANUALLY!
+
+.. _api_fluid_dygraph_GRUCell:
+
+GRUCell
+-------
+
+..  autoclass:: paddle.fluid.dygraph.GRUCell
+    :members:
+    :noindex:
+

doc/fluid/api/dygraph/LSTMCell.rst

+..  THIS FILE IS GENERATED BY `gen_doc.{py|sh}`
+    !DO NOT EDIT THIS FILE MANUALLY!
+
+.. _api_fluid_dygraph_LSTMCell:
+
+LSTMCell
+--------
+
+..  autoclass:: paddle.fluid.dygraph.LSTMCell
+    :members:
+    :noindex:
+

doc/fluid/api/tensor/random/rand.rst

+..  THIS FILE IS GENERATED BY `gen_doc.{py|sh}`
+    !DO NOT EDIT THIS FILE MANUALLY!
+
+.. _api_tensor_random_rand:
+
+rand
+----
+
+..  autofunction:: paddle.tensor.random.rand
+    :noindex:
+