Update docstring to reflect correct units (googleapis#5277)

Author: wyardley

storage/google/cloud/storage/blob.py

@@ -112,8 +112,9 @@ class Blob(_PropertyMixin):
     :param bucket: The bucket to which this blob belongs.
 
     :type chunk_size: int
-    :param chunk_size: The size of a chunk of data whenever iterating (1 MB).
-                       This must be a multiple of 256 KB per the API
+
+    :param chunk_size: The size of a chunk of data whenever iterating (in
+                       bytes). This must be a multiple of 256 KB per the API
                        specification.
 
     :type encryption_key: bytes

storage/google/cloud/storage/bucket.py

@@ -183,8 +183,8 @@ def blob(self, blob_name, chunk_size=None, encryption_key=None):
 
         :type chunk_size: int
         :param chunk_size: The size of a chunk of data whenever iterating
-                           (1 MB). This must be a multiple of 256 KB per the
-                           API specification.
+                           (in bytes). This must be a multiple of 256 KB per
+                           the API specification.
 
         :type encryption_key: bytes
         :param encryption_key: