setup: configure setuptools_scm for proper version

When I built the v2.0.0 release, the version number came out as 0.0.0
There was no release of django-simple-menu before, while on Jazzband, so
I guess it never worked!

I looked at setuptools_scm configuration for django-redshift-backend for
a working configuration and I verified it now works correctly

Author: mbeijen

pyproject.toml

@@ -1,6 +1,7 @@
 [build-system]
-requires = ["setuptools", "setuptools_scm"]
-build-backend = "setuptools.build_meta"
+requires = ["setuptools>=42", "wheel", "setuptools_scm[toml]>=3.4"]
 
 [tool.setuptools_scm]
-version_scheme = "post-release"
+# this empty section means: use_scm_version=True
+version_scheme = "guess-next-dev"
+local_scheme = "no-local-version"

setup.cfg

@@ -35,3 +35,5 @@ python_requires = >=3.6,<4.0
 install_requires =
     Django>=2.2
     importlib_metadata
+setup_requires =
+    setuptools_scm