[build2] Dockerfiles and Docker Images

[Markus Pawellek]

Hello,

some time ago, I have created some basic Docker images for build2.
Their appropriate Dockerfiles can be found by using the following links.
All of them are also published on Docker Hub.

- https://github.com/lyrahgames/docker-ubuntu-gcc-build2
- https://github.com/lyrahgames/docker-clang-build2
- https://github.com/lyrahgames/docker-gcc-build2

These images are of course not perfect and may contain some flaws
but I have given my best to use Docker's best practices,
like multistage builds and one-layer installations.
I have used them myself for CI servers and web programming
and would appreciate any comments and suggestions for improvements.

I am not sure if you or other people are already working on some Docker images
because I could not find any issues on this.
Maybe you are interested in providing an official Dockerfile or Docker image.
In this case, these Dockerfiles may be useful to you.
I would be glad to help.

Greetings
Markus