Add __main__ for post install

jenshnielsen · jenshnielsen · commit d2f77a93c4f9 · 2022-04-11T21:16:45.000+02:00
So post install can be executed as

`python -m win32.lib.postinstall`
diff --git a/win32/Lib/postinstall/__main__.py b/win32/Lib/postinstall/__main__.py
@@ -0,0 +1,3 @@
+from win32.lib.postinstall.pywin32_postinstall import main
+
+main()

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	`+from win32.lib.postinstall.pywin32_postinstall import main`
	`2`	`+`
	`3`	`+main()`