setup.py: Specify compatible Python versions

Signed-off-by: Otavio Salvador <[email protected]>

Author: otavio

setup.py

@@ -15,6 +15,7 @@
     author='O.S. Systems Software LTDA',
     author_email='[email protected]',
     url='http://www.ossystems.com.br',
+    python_requires='>=3.5, <4',
     license='MIT',
     classifiers=[
         "License :: OSI Approved :: MIT License",