include README.md contents in Python wheel long_description; add dist_check step to the GA workflow

Author: slayoo

.github/workflows/tests+artifacts.yml

@@ -72,3 +72,15 @@ jobs:
 #        uses: mxschmitt/action-tmate@v3
 #        with:
 #          limit-access-to-actor: true
+
+  dist_check:
+    runs-on: ubuntu-latest
+    needs: [build]
+    steps:
+    - uses: actions/setup-python@v2
+    - run: pip install twine
+    - uses: actions/download-artifact@v2
+      with:
+        name: dist
+        path: dist
+    - run: twine check --strict dist/*

setup.py

@@ -8,7 +8,7 @@
 import re
 import subprocess
 import sys
-
+from pathlib import Path
 from setuptools import Extension, setup
 from setuptools.command.build_ext import build_ext
 
@@ -128,7 +128,8 @@ def build_extension(self, ext):  # pylint: disable=too-many-branches
     author="Sylwester Arabas",
     author_email="[email protected]",
     description="Python interface to PartMC",
-    long_description="",
+    long_description=(Path(__file__).parent / "README.md").read_text(),
+    long_description_content_type="text/markdown",
     ext_modules=[CMakeExtension("PyPartMC")],
     cmdclass={"build_ext": CMakeBuild},
     zip_safe=False,