Update bash.md

Add both stdout and stderr to null

bash.md

@@ -525,6 +525,7 @@ python hello.py >> output.txt  # stdout to (file), append
 python hello.py 2> error.log   # stderr to (file)
 python hello.py 2>&1           # stderr to stdout
 python hello.py 2>/dev/null    # stderr to (null)
+python hello.py &>/dev/null    # stdout and stderr to (null)
 ```
 
 ```bash