Append license to file header

[shingon]

wait-for-it.sh is single file shell script. So, if the license is in file header, the users are very useful for deploying their system.

[msabramo]

This needs to be updated, as it has a merge conflict now, but I very much like the idea. In fact, I was thinking of submitting a PR for the same change myself before I saw this PR.

[msabramo]

Oh, I would add one more thing. I would add the LICENSE to wait-for-it.sh as was done here, so folks can copy the one file into their repo and know the license, but I would also add the URL of the git repository, https://github.com/vishnubob/wait-for-it, so that folks know where it came from and where to go to look for updates, or if they want to contribute fixes or enhancements.