Clarify how to use the different base image versions. about docker-nginx-unprivileged

[alessfg]

Hey @syker-uk!

Both images seem to be running correctly on my end and I can't reproduce your issue. There is supposed to be no user since these are unprivileged images (the system running the container decides what the user is). Are you perhaps changing the default config file?

Re how to use the alpine-slim version, I am not entirely sure we need to add more info? I am not entirely sure what shape that info would take? It's as simple as running docker run -d nginxinc/nginx-unprivileged:1.24.0-alpine-slim -- and I am a bit wary of adding docs re how to use Docker to this repo since this is not the place such docs should live. I can add a little table detailing which tags are available but that's about the extent of what I want to do.

Re how the images are built, I am hoping to do a more detailed write up re how to locally build and test the images, but I don't have a realistic ETA for it. The tl;dr is that the alpine-perl image uses the alpine NGINX image to speed up the build process. Same thing happens between the alpine NGINX image and the alpine-slim image.