fix examples for freeze_support() issue on windows

[deounix]

Sanic on windows should always run inside:

if __name__ == "__main__": app.run()

Check this: https://docs.python.org/2/library/multiprocessing.html#the-process-class

For an explanation of why (on Windows) the if __name__ == '__main__' part is necessary, see [Programming guidelines]

Without the __name__ == "__main__" it throw this error on windows:

RuntimeError:
        An attempt has been made to start a new process before the
        current process has finished its bootstrapping phase.

        This probably means that you are not using fork to start your
        child processes and you have forgotten to use the proper idiom
        in the main module:

            if __name__ == '__main__':
                freeze_support()
                ...

        The "freeze_support()" line can be omitted if the program
        is not going to be frozen to produce an executable.

On Linux, Mac it's run normally.
I think we should update the docs to notify the users about this issue.

[SaidBySolo]

Good catch

[codecov]

Codecov Report

Patch coverage: 100.000% and project coverage change: +0.006 🎉

Comparison is base (af67801) 88.938% compared to head (1ce41b9) 88.944%.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #2741       +/-   ##
=============================================
+ Coverage   88.938%   88.944%   +0.006%     
=============================================
  Files           92        92               
  Lines         6952      6956        +4     
  Branches      1185      1185               
=============================================
+ Hits          6183      6187        +4     
  Misses         527       527               
  Partials       242       242               

Impacted Files	Coverage Δ
sanic/application/logo.py	100.000% <100.000%> (ø)
sanic/application/motd.py	97.849% <100.000%> (ø)
sanic/asgi.py	91.729% <100.000%> (+0.062%)	⬆️
sanic/helpers.py	100.000% <100.000%> (ø)
sanic/log.py	100.000% <100.000%> (ø)
sanic/mixins/startup.py	92.753% <100.000%> (ø)

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