Add Docker support

[amaurycannesson]

It could be usefull to have this great tool packaged in a docker image.

I can make a pull request, I have a Dockerfile ready for this.

[mdestafadilah]

PHP 7 ?

[naikrovek]

I would like to second this. I have no idea how to set up PHP, I don't use PHP, and I don't want to pollute my system with a language and libraries & modules that I don't regularly use, so I am going to try to set up my own Dockerfile for this, but it would be lovely if this was supported. Surely the maintainer can get this going faster than I can. I don't care what version of PHP is installed in there, of course, as long as the utilities work.

I will also say that the maintainer owes me nothing, and whether or not they choose to do this is entirely up to them. I do not wish to make the life of any maintainer worse in any way.