allow running compose from git

with:

```
$ git clone docker/compose && cd compose
$ export PYTHONPATH="$PWD:$PYTHONPATH"
$ python -m compose --help
```

Signed-off-by: Tomas Tomecek <[email protected]>

compose/__main__.py

@@ -0,0 +1,3 @@
+from compose.cli.main import main
+
+main()