docs(storage): add documentation about upload and download (#168)

Author: HemangChothani

google/cloud/storage/blob.py

@@ -882,6 +882,10 @@ def download_to_file(
         The ``encryption_key`` should be a str or bytes with a length of at
         least 32.
 
+        If the :attr:`chunk_size` of a current blob is `None`, will download data
+        in single download request otherwise it will download the :attr:`chunk_size`
+        of data in each request.
+
         For more fine-grained control over the download process, check out
         `google-resumable-media`_. For example, this library allows
         downloading **parts** of a blob rather than the whole thing.
@@ -1574,7 +1578,7 @@ def _do_upload(
     ):
         """Determine an upload strategy and then perform the upload.
 
-        If the size of the data to be uploaded exceeds 5 MB a resumable media
+        If the size of the data to be uploaded exceeds 8 MB a resumable media
         request will be used, otherwise the content and the metadata will be
         uploaded in a single multipart upload request.
 
@@ -1704,6 +1708,10 @@ def upload_from_file(
         The ``encryption_key`` should be a str or bytes with a length of at
         least 32.
 
+        If the size of the data to be uploaded exceeds 8 MB a resumable media
+        request will be used, otherwise the content and the metadata will be
+        uploaded in a single multipart upload request.
+
         For more fine-grained over the upload process, check out
         `google-resumable-media`_.