[docs] Update set_default_(tensor_|d)type docs (#6843)

* update set_default_(tensor_|d)type docs

* make ndarray display nicer
diff --git a/torch/__init__.py b/torch/__init__.py
index 3bab31f..5fac95a 100644
--- a/torch/__init__.py
+++ b/torch/__init__.py
@@ -129,18 +129,22 @@
 
 
 def set_default_tensor_type(t):
-    r"""Sets the default ``torch.Tensor`` type to type :attr:`t`.
+    r"""Sets the default ``torch.Tensor`` type to floating point tensor type
+    :attr:`t`. This type will also be used as default floating point type for
+    type inference in :func:`torch.tensor`.
 
-    The default tensor type is initially ``"torch.FloatTensor"``.
+    The default tensor type is initially ``torch.FloatTensor``
 
     Args:
-        t (type or string): the tensor type or its name
+        t (type or string): the floating point tensor type or its name
 
     Example::
 
-        >>> torch.set_default_tensor_type("torch.FloatTensor")
-        >>> torch.tensor([1.2, 3])
-        tensor([ 1.2000,  3.0000])
+        >>> torch.tensor([1.2, 3]).dtype  # default is float32
+        torch.float32
+        >>> torch.set_default_tensor_type(torch.DoubleTensor)
+        >>> torch.tensor([1.2, 3]).dtype  # floating point tensor
+        torch.float64
 
     """
     if isinstance(t, _string_classes):
@@ -149,16 +153,20 @@
 
 
 def set_default_dtype(d):
-    r"""Sets the default ``torch.dtype`` type to type :attr:`d`.
+    r"""Sets the default floating point dtype to :attr:`d`. This type will be
+    used as default floating point type for type inference in
+    :func:`torch.tensor`.
 
     Args:
-        d (torch.dtype): the dtype to make the default
+        d (:class:`torch.dtype`): the floating point dtype to make the default
 
     Example::
 
+        >>> torch.tensor([1.2, 3]).dtype  # default is float32
+        torch.float32
         >>> torch.set_default_dtype(torch.double)
-        >>> torch.tensor([1.2, 3], device='cpu')
-        tensor([ 1.2000,  3.0000])
+        >>> torch.tensor([1.2, 3]).dtype
+        torch.float64
     """
     _C._set_default_dtype(d)
 
diff --git a/torch/_torch_docs.py b/torch/_torch_docs.py
index 4e84350..a9def09 100644
--- a/torch/_torch_docs.py
+++ b/torch/_torch_docs.py
@@ -1465,9 +1465,9 @@
 
 Creates a :class:`Tensor` from a :class:`numpy.ndarray`.
 
-The returned tensor and `ndarray` share the same memory. Modifications to the
-tensor will be reflected in the `ndarray` and vice versa. The returned tensor
-is not resizable.
+The returned tensor and :attr:`ndarray` share the same memory. Modifications to
+the tensor will be reflected in the :attr:`ndarray` and vice versa. The returned
+tensor is not resizable.
 
 Example::
 
@@ -3476,12 +3476,12 @@
     :func:`torch.tensor` always copies :attr:`data`. If you have a Tensor
     ``data`` and want to avoid a copy, use :func:`torch.Tensor.requires_grad_`
     or :func:`torch.Tensor.detach`.
-    If you have a numpy array and want to avoid a copy, use
+    If you have a NumPy ``ndarray`` and want to avoid a copy, use
     :func:`torch.from_numpy`.
 
 Args:
     data (array_like): Initial data for the tensor. Can be a list, tuple,
-        numpy array, scalar, and other types.
+        NumPy ``ndarray``, scalar, and other types.
     dtype (:class:`torch.dtype`, optional): the desired data type of returned tensor.
         Default: if None, infers data type from :attr:`data`.
     device (:class:`torch.device`, optional): the desired device of returned tensor.