Add composer by default

[insign]

I truly understand that you want a very simple and clean image but have composer looks like a must. I saw in the documentation how to add but keeps the sensation that is so needed because even small projects should rely on composer to keeps things tidy.

[TrafeX]

Hi @insign,

Of course most projects would benefit from Composer. But there are more ways to install the Composer dependencies than to do that in the container. And there are still enough PHP projects that don't rely on Composer for the dependencies. Think of WordPress, PHPMyAdmin and others. So it's not a must and you can easily add it to your own copy of this image.