Add ~/.config/atuin deletion to uninstall docs

[justinmayer]

Since the ~/.config/atuin directory (and configuration files within) appear to be created when Atuin is first invoked, this directory should be added to the list of directories to be deleted in the uninstall documentation.

[justinmayer]

Also, it seems Atuin also installs shell-specific configuration files that must be removed in order to prevent errors on subsequent shell startup. For example, on Fish shell:

source: Error encountered while sourcing file '/home/myuser/.atuin/bin/env.fish':
source: No such file or directory

In this case it seems Atuin installed a file at ~/.config/fish/conf.d/atuin.env.fish, which presumably should also be added to the list of files that must be removed.

What other shell configuration files might also need to be removed, for example on Zsh or Bash?