[seL4] Docker / gnat

Hello, I converted over from my old development environment to the docker-based version this weekend. Everything worked fine, except for one thing. I was using the gnat-6-aarch64-linux-gnu and gnat-6-arm-linux-gnueabihf packages to compile Ada code. Ada is not installed by default in the docker container. I can install it, but it goes away when the container terminates. I am brand new to docker. Can I make these changes permanent myself or does it require the container provider to do so?

Thanks! Dave