Update README

Subjective · Subjective · commit 9b9ca936a487 · 2023-09-05T18:24:12.000-07:00
diff --git a/README.md b/README.md
@@ -37,6 +37,8 @@ You may also obtain specific shell configuration using.
 leetcode completions fish
 ```
 
+If no argument is provided, the shell is inferred from the `SHELL` environment variable.
+
 </details>
 
 ## Usage
