The install instructions for OSX is outdated for M1 Macs.

[peauc]

The README.md states

Add this to your ~/.config/fish/config.fish:

if test (uname -s) = "Darwin"
  set -gx PATH /usr/local/opt/coreutils/libexec/gnubin $PATH
  set -gx PATH /usr/local/opt/gnu-sed/libexec/gnubin $PATH
end

However as per brew documentation:

[Brew installation folder...]:
/usr/local for macOS on Intel,
/opt/homebrew for macOS on Apple Silicon/ARM, and
/home/linuxbrew/.linuxbrew for Linux.

For my installation I had to change the path to ( and i added fish_add_path )

if test (uname -s) = 'Darwin' 
   and test (uname -p) = "arm"
  fish_add_path -p /opt/homebrew/opt/coreutils/libexec/gnubin
  fish_add_path -p /opt/homebrew/opt/gnu-sed/libexec/gnubin
end

I could draft a PR tackling this change. Thank you for your work on this amazing theme.