add shebang in pre-push hook script

README.md

@@ -27,7 +27,7 @@ As you may know, the [`UUID`](http://www.ietf.org/rfc/rfc4122.txt) generated by
 ### How to use
 --------------
 1. Put **xUnique.py** file in your project repository somewhere and add it as track file via `git add path/to/xUnique.py`, so all members could use the same script
-2. create a git hook like `echo "python2 /absolute/path/to/xUnique.py /absolute/path/to/MyProject.xcodeproj" > .git/hooks/pre-push`
+2. create a git hook like `{ echo '#!/bin/sh'; echo 'python2 /absolute/path/to/xUnique.py /absolute/path/to/MyProject.xcodeproj'; } > .git/hooks/pre-push`
 3. Add permission `chmod 555 .git/hooks/pre-push` 
     * use hook `pre-push` instead of `pre-commit` is a safe consideration: you decide to commit the newly generated project file or not
 4. In all your branches, uniquify `project.pbxproj` file in either way: