Add support for checking folders

[smjonas]

Thanks for this useful project! What do you think about adding support for folders when using the nerdfix check / nerdfix fix commands in which case the command would be applied to all the files in the directory recursively? This would allow something like nerdfix check ~/.local/share/nvim to check all Nvim configuration files.

[loichyan]

I added --recursive in #6, but it's recommended to use nerdfix check $(fd -t f . ~/.local/share/nvim) to exclude some hidden directories (like .git, which contains many binary files and causes many non-UTF-8 errors).