docs(storage): add description and example to retrieve the hash of blob (googleapis#75)

Fixes googleapis#54

Author: HemangChothani

google/cloud/storage/blob.py

@@ -1874,13 +1874,32 @@ def update_storage_class(self, new_class, client=None):
     crc32c = _scalar_property("crc32c")
     """CRC32C checksum for this object.
 
+    This returns the blob's CRC32C checksum. To retrieve the value, first use a
+    reload method of the Blob class which loads the blob's properties from the server.
+
     See `RFC 4960`_ and `API reference docs`_.
 
     If not set before upload, the server will compute the hash.
 
     :rtype: str or ``NoneType``
 
     .. _RFC 4960: https://tools.ietf.org/html/rfc4960#appendix-B
+
+    Example:
+            Retrieve the crc32c hash of blob.
+
+            >>> from google.cloud import storage
+            >>> client = storage.Client()
+            >>> bucket = client.get_bucket("my-bucket-name")
+            >>> blob = bucket.blob('my-blob')
+
+            >>> blob.crc32c  # return None
+            >>> blob.reload()
+            >>> blob.crc32c  # return crc32c hash
+
+            >>> # Another approach
+            >>> blob = bucket.get_blob('my-blob')
+            >>> blob.crc32c  # return crc32c hash
     """
 
     @property
@@ -1954,13 +1973,32 @@ def id(self):
     md5_hash = _scalar_property("md5Hash")
     """MD5 hash for this object.
 
+    This returns the blob's MD5 hash. To retrieve the value, first use a
+    reload method of the Blob class which loads the blob's properties from the server.
+
     See `RFC 1321`_ and `API reference docs`_.
 
     If not set before upload, the server will compute the hash.
 
     :rtype: str or ``NoneType``
 
     .. _RFC 1321: https://tools.ietf.org/html/rfc1321
+
+    Example:
+            Retrieve the md5 hash of blob.
+
+            >>> from google.cloud import storage
+            >>> client = storage.Client()
+            >>> bucket = client.get_bucket("my-bucket-name")
+            >>> blob = bucket.blob('my-blob')
+
+            >>> blob.md5_hash  # return None
+            >>> blob.reload()
+            >>> blob.md5_hash  # return md5 hash
+
+            >>> # Another approach
+            >>> blob = bucket.get_blob('my-blob')
+            >>> blob.md5_hash  # return md5 hash
     """
 
     @property