Dockerfile

[Kukunin]

Add Dockerfile to build docker images

[pcercuei]

Please squash the commits, then sign-off the result (git commit -s), then I'll merge it.

[Kukunin]

Hi @pcercuei sorry for the delay. I want to test the dockerfiles so it works, then I'll build the latest docker images and will push it the PR as you wanted (a single signed commit)

[Kukunin]

I've finished this PR after a year ) However, I have a couple of concerns.
The Dockerfile contains only toolchain, which I believe might be useful in some cases. The main advantage over archived toolchains is that it has all build dependencies installed. However, if one builds a lot, it's still better to configure the toolchain and all dependencies once on a host.

Having the toolchain residing in Docker wouldn't make buildroot build faster since it still needs to compile a lot of stuff. Frankly, I even don't know how to leverage the outside toolchain for buildroot, and how much time it would save.

I thought about keeping compiled objects in a docker image, so one shouldn't compile the whole buildroot if he needs to make a change. But all compiled objects are about 15gb, so I doubt it's too much more convenient to download 15gb over building for hours.

Anyway, it's the first step, and I believe it's still worth including in the repo so others can leverage Docker and working Dockerfile