Override install requirements when building with Read the Docs

Signed-off-by: Vasilis Tsiligiannis <acinonyx@openwrt.gr>

setup.py

@@ -1,8 +1,15 @@
+from os import getenv
+
 from setuptools import setup
 
 import versioneer
 
-setup(
-    version=versioneer.get_version(),
-    cmdclass=versioneer.get_cmdclass(),
-)
+setup_args = {
+    'version': versioneer.get_version(),
+    'cmdclass': versioneer.get_cmdclass(),
+}
+
+if getenv('READTHEDOCS') == 'True':
+    setup_args['install_requires'] = ['setuptools']
+
+setup(**setup_args)