setup.cfg: Mark setuptools as required

dcbaker · jpakkane · commit cd79ec2839dd · 2020-04-21T00:40:19.000+03:00
It's required, lets just document it as such.
diff --git a/setup.cfg b/setup.cfg
@@ -30,6 +30,8 @@ long_description = Meson is a cross-platform build system designed to be both as
 
 [options]
 python_requires = >= 3.5.2
+setup_requires =
+  setuptools
 
 [options.extras_require]
 progress =
