setup.py: block unsafe 'upload', say to use twine instead

setup.py

@@ -130,8 +130,10 @@ def check_external_program(
     print('Found {program} {found_version}'.format(
             program=program, found_version=found_version))
 
+
 command = next((arg for arg in sys.argv[1:] if not arg.startswith('-')), '')
 
+
 if command.startswith('install') or \
         command in ['check', 'test', 'nosetests', 'easy_install', 'egg_info']:
     check_external_program(
@@ -163,6 +165,11 @@ if command.startswith('install') or \
         version_check_args=['--version']
     )
 
+
+if 'upload' in sys.argv[1:]:
+    print('Use twine to upload the package - setup.py upload is insecure')
+    sys.exit(1)
+
 setup(
     name='ocrmypdf',
     version='3.0rc4',  # also update: release notes, main.py