Update fish completion installation
diff --git a/INSTALL.md b/INSTALL.md
index 4f6f5db..72aa711 100644
--- a/INSTALL.md
+++ b/INSTALL.md
@@ -284,9 +284,11 @@
 To install the completions for fish, run
 
 ```
-sudo cp alacritty-completions.fish $__fish_datadir/vendor_completions.d/alacritty.fish
+sudo cp alacritty-completions.fish $__fish_data_dir/vendor_completions.d/alacritty.fish
 ```
 
+**Note:** For fish versions below 3.0 `$__fish_datadir` must be used instead.
+
 ## Terminfo
 
 The terminfo database contains entries describing the terminal