Fix config dir typo in doc - #6512

Hi there @pllim 👋 - thanks for the pull request! I'm just a friendly 🤖 that checks for issues related to the changelog and making sure that this pull request is milestoned and labelled correctly. This is mainly intended for the maintainers, so if you are not a maintainer you can ignore this, and a maintainer will let you know if any action is required on your part 😃.

Everything looks good from my point of view! 👍

Thanks @pllim! PRs like this are absolutely fine for 2.0.x, they are always clean backports thus add basically no overhead, while keeping the docs cleaner and nicer for LST.

Merging as no need to wait for CI.

I think the previous sentence was more correct: when $XDG_CONFIG_HOME is not defined, many software put their config in ~/.config by default. But there are also many others that put the config in ~/.<software>, so maybe this sentence is not needed at all, it just adds confusion.

On my RHEL7 machine, it defaults to ~/.astropy/config. I cannot find any ~/.config/astropy although ~/.config does exist and populated with other stuff.

@saimn , feel free to submit a follow-up if you think this is inaccurate.

@pllim - Understood, but the note you modified is about the behavior of most Linux applications. The paragraph just above mention that the default for Astropy is $HOME/.astropy/config. That's why I think that the note is confusing and could be removed. (I can submit a PR for this later if this makes sense)

@saimn , sure, please do. The note was indeed confusing because it was not the behavior I actually observed for Astropy.