Disclaim typing annotations in an example

Author: jwnimmer-tri

pyguide.md

@@ -2317,6 +2317,11 @@ def fetch_smalltable_rows(table_handle: smalltable.Table,
     """
 ```
 
+<span class="drake">
+In the above example, note that the typing annotations on the function
+signature are not required in Drake.
+</span>
+
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