add __main__.py file

I'm adding this file, so you can call pkgdev using `python -m pkgdev`.

Signed-off-by: Arthur Zamarin <arthurzam@gentoo.org>

Author: arthurzam

src/pkgdev/__main__.py

@@ -0,0 +1,4 @@
+from .scripts import run
+
+if __name__ == '__main__':
+    run('pkgdev')