Add squid to $PATH and add squid to CMD

[sickcodes]

Doesn't change any existing scripts.

-d detached mode instead of &

Allows use of -e CONF=squid.conf.https_port when docker running

[salrashid123]

LGTM. thanks

added a formatting comment. The default behavior of running the container will change though

eg, running docker run -it -p 3128:3128 docker.io/salrashid123/squidproxy used to drop you into a shell

and after this, the same command will auto-launch squid in forward mode.

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i don't see it as a big deal since the docs stated you should invoke /bin/bash to get a shell anyway.