Make 'python -m black' work (#1460)

README.md

@@ -58,6 +58,12 @@ To get started right away with sensible defaults:
 black {source_file_or_directory}
 ```
 
+You can run _Black_ as a package if running it as a script doesn't work:
+
+```sh
+python -m black {source_file_or_directory}
+```
+
 ### Command line options
 
 _Black_ doesn't provide many options. You can list them by running `black --help`:

src/black/__main__.py

@@ -0,0 +1,3 @@
+from black import patched_main
+
+patched_main()