add __main__ file for convenient CLI usage

osbuild/__main__.py

@@ -35,3 +35,7 @@ def main():
         print()
         print(f"{RESET}{BOLD}{RED}{error.name} failed with code {error.returncode}{RESET}")
         sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()

setup.py

@@ -7,11 +7,11 @@ setuptools.setup(
     description="A build system for OS images",
     packages=["osbuild"],
     entry_points={
-        "console_scripts": ["osbuild = osbuild.executable:main"]
+        "console_scripts": ["osbuild = osbuild.__main__:main"]
     },
     data_files=[
         ("/usr/lib/osbuild", ["osbuild-run"]),
         ("/usr/lib/osbuild/stages", glob.glob("./stages/*")),
         ("/usr/lib/osbuild/assemblers", glob.glob("./assemblers/*"))
     ]
-)
+)