Why not use the latest versions available here?

I'm not sure where "here" is? Maybe some document...I just updated this PR based on my experience. The latest versions of Elixir and Erlang did not work for my use case, and I spent a bit of time just changing versions and getting further until I had a working app. I have the repo elsewhere if any file will help further.

But if you are removing the defaults and requiring an explicit config file, then I agree with that move. However, if there were no defaults, then I wouldn't have gotten a little farther by removing my custom config files and seeing my issue probably related to version compatibility with my project dependencies.

I do foresee people with different projects trying to use the same "default versions" mentioned in a readme or file, failing the build, and then giving up. At least that was my experience. So, that's why I wanted to add a note to the potential future me to "not give up until you've played around with versions. Look at X to guide you" with X being the supported versions section.

Of course, you might say, "that's already in there dude, RTFM." but I guarantee you a lot of devs will not read the whole thing and skip around to the config file options. I tend to try and over document things, if that makes sense.

This shouldn't be needed now that we are removing default versions here
#209