Modify .values docs to process issue #10364.

Author: sstanovnik

pandas/core/generic.py

@@ -2887,7 +2887,8 @@ def as_matrix(self, columns=None):
 
         e.g. If the dtypes are float16 and float32, dtype will be upcast to
         float32.  If dtypes are int32 and uint8, dtype will be upcase to
-        int32.
+        int32. By numpy.find_common_type convention, mixing int64 and uint64
+        will result in a flot64 dtype.
 
         This method is provided for backwards compatibility. Generally,
         it is recommended to use '.values'.
@@ -2913,8 +2914,9 @@ def values(self):
         with care if you are not dealing with the blocks.
 
         e.g. If the dtypes are float16 and float32, dtype will be upcast to
-        float32.  If dtypes are int32 and uint8, dtype will be upcase to
-        int32.
+        float32.  If dtypes are int32 and uint8, dtype will be upcast to
+        int32. By numpy.find_common_type convention, mixing int64 and uint64
+        will result in a flot64 dtype.
         """
         return self.as_matrix()