Update readme

README.md

@@ -36,7 +36,19 @@ cargo install --path .
 
 ## Usage
 
-Run `scooter` in a terminal to launch Scooter. You can then enter some text to search with and text to replace matches with, toggle on or off fixed strings, and enter a regex pattern that filenames must match. A more extensive set of keymappings will be shown at the bottom of the window: these vary slightly depending on the screen you're on.
+Run
+
+```sh
+scooter
+```
+
+in a terminal to launch Scooter. By default the current directory is used to search and replace in, but you can pass in a directory as the first argument to override this behaviour:
+
+```sh
+scooter ../foo/bar`
+```
+
+You can then enter some text to search with and text to replace matches with, toggle on or off fixed strings, and enter a regex pattern that filenames must match. A more extensive set of keymappings will be shown at the bottom of the window: these vary slightly depending on the screen you're on.
 
 ## Contributing