Merge pull request pytorch#30 from SsnL/module_name_dot

Update migration guide on new constraints of module/buffer/parameter names

Author: soumith

_posts/2018-04-22-0_4_0-migration-guide.md

@@ -11,6 +11,7 @@ Welcome to the migration guide for PyTorch 0.4.0. In this release we introduced
 * Deprecation of the ``volatile`` flag
 * ``dtypes``, ``devices``, and Numpy-style ``Tensor`` creation functions
 * Writing device-agnostic code
+* New edge-case constraints on names of submodules, parameters, and buffers in ``nn.Module``
 
 
 ## Merging [``Tensor``](http://pytorch.org/docs/0.4.0/tensors.html) and ``Variable`` and classes
@@ -299,6 +300,10 @@ input = data.to(device)
 model = MyModule(...).to(device)
 ```
 
+## New edge-case constraints on names of submodules, parameters, and buffers in ``nn.Module``
+
+`name` that is an empty string or contains `"."` is no longer permitted in `module.add_module(name, value)`, `module.add_parameter(name, value)` or `module.add_buffer(name, value)` because such names may cause lost data in the `state_dict`. If you are loading a checkpoint for modules containing such names, please update the module definition and patch the `state_dict` before loading it.
+
 ## Code Samples (Putting it all together)
 
 To get a flavor of the overall recommended changes in 0.4.0, let's look at a quick example for a common code pattern in both 0.3.1 and 0.4.0: