Detect Homebrew location for Intel support

The hardcoded `/opt/homebrew/bin/brew` path only works on
Apple Silicon Macs. Intel Macs install Homebrew to
`/usr/local/bin/brew`. Check both paths before eval-ing
shellenv.

Closes #781

Author: purinkle

zshrc

@@ -34,7 +34,11 @@ _load_settings() {
 }
 _load_settings "$HOME/.zsh/configs"
 
-eval "$(/opt/homebrew/bin/brew shellenv)"
+if [ -x /opt/homebrew/bin/brew ]; then
+  eval "$(/opt/homebrew/bin/brew shellenv)"
+elif [ -x /usr/local/bin/brew ]; then
+  eval "$(/usr/local/bin/brew shellenv)"
+fi
 
 export PATH="${ASDF_DATA_DIR:-$HOME/.asdf}/shims:$PATH"