put_image example using bytes-like object (#172)

* put_image example using bytes-like object

* Update docs/guide.rst

Co-authored-by: WangWeimin <wang0.618@qq.com>

Co-authored-by: WangWeimin <wang0.618@qq.com>

docs/guide.rst

@@ -215,7 +215,8 @@ Using output functions, you can output a variety of content, such as text, table
     ## ----
 
     # Image Output
-    put_image('some-image.png')  # ..doc-only
+    put_image(open('/path/to/some/image.png', 'rb').read())  # local image # ..doc-only
+    put_image('http://example.com/some-image.png')  # internet image # ..doc-only
     put_image('https://www.python.org/static/img/python-logo.png')  # ..demo-only
     ## ----
 
@@ -796,4 +797,4 @@ ask yourself a question: What would I do if it is in a terminal program?
 If you already have the answer, it can be done in the same way with PyWebIO. If the problem persists or the solution is
 not good enough, you can consider the :ref:`callback mechanism <callback>` or  :doc:`pin <./pin>` module.
 
-OK, Have fun with PyWebIO!
+OK, Have fun with PyWebIO!