Merge pull request #647 from untitaker/print_in_cgi

Added hint about print statements in CGI.

docs/deploying/cgi.rst

@@ -16,6 +16,10 @@ Engine`_, where execution happens in a CGI-like environment.
    not called because this will always start a local WSGI server which
    we do not want if we deploy that application to CGI / app engine.
 
+   With CGI, you will also have to make sure that your code does not contain
+   any ``print`` statements, or that ``sys.stdin`` is overridden by something
+   that doesn't write into the HTTP response.
+
 Creating a `.cgi` file
 ----------------------