[docs] add docstring in torch.cuda.get_device_properties (#49792)

Summary:
Fixes #49737

Added docstring in `torch.cuda.get_device_properties`
Added the `Returns` in `torch.cuda.get_device_name`

Pull Request resolved: #49792

Reviewed By: mruberry

Differential Revision: D25784046

Pulled By: ngimel

fbshipit-source-id: f88da02147f92c889398957fcaf22961d3bb1062

torch/cuda/__init__.py

@@ -271,6 +271,9 @@ def get_device_name(device: Optional[_device_t] = None) -> str:
             name. This function is a no-op if this argument is a negative
             integer. It uses the current device, given by :func:`~torch.cuda.current_device`,
             if :attr:`device` is ``None`` (default).
+
+    Returns:
+        str: the name of the device
     """
     return get_device_properties(device).name
 
@@ -293,6 +296,15 @@ def get_device_capability(device: Optional[_device_t] = None) -> Tuple[int, int]
 
 
 def get_device_properties(device: _device_t) -> _CudaDeviceProperties:
+    r"""Gets the properties of a device.
+
+    Args:
+        device (torch.device or int or str): device for which to return the
+            properties of the device.
+
+    Returns:
+        _CudaDeviceProperties: the properties of the device
+    """
     _lazy_init()  # will define _get_device_properties
     device = _get_device_index(device, optional=True)
     if device < 0 or device >= device_count():