Add comment where to find classifiers

pyproject.toml

@@ -9,6 +9,7 @@ description = "Django components that know how to render themselves."
 readme = "README.md"
 license = {file = "LICENSE"}
 classifiers = [
+    # https://pypi.org/classifiers/
     "Development Status :: 3 - Alpha",
     "Intended Audience :: Developers",
     "License :: OSI Approved :: BSD License",