docs: open file-like objects in byte mode for uploads (#824)

File-like objects should be opened in binary mode for `blob.upload_from_file()`
- cpython standard library accorded with [RFC 2616 Section 3.7.1](https://datatracker.ietf.org/doc/html/rfc2616#section-3.7.1) states the text default charset of iso-8859-1
- add clarifying notes in docstring
- update code sample

Fixes #818 🦕

google/cloud/storage/blob.py

@@ -2456,7 +2456,7 @@ def upload_from_file(
         to that project.
 
         :type file_obj: file
-        :param file_obj: A file handle open for reading.
+        :param file_obj: A file handle opened in binary mode for reading.
 
         :type rewind: bool
         :param rewind:

samples/snippets/storage_upload_from_stream.py

@@ -25,8 +25,8 @@ def upload_blob_from_stream(bucket_name, file_obj, destination_blob_name):
 
     # The stream or file (file-like object) from which to read
     # import io
-    # file_obj = io.StringIO()
-    # file_obj.write("This is test data.")
+    # file_obj = io.BytesIO()
+    # file_obj.write(b"This is test data.")
 
     # The desired name of the uploaded GCS object (blob)
     # destination_blob_name = "storage-object-name"