Use a file in the no-shell grep example (#937)

* Use a file in the no-shell grep example

* Use recursive grep in the no-shell example

README.md

@@ -105,7 +105,7 @@ If you want to run a benchmark *without an intermediate shell*, you can use the
 option. This is helpful for very fast commands (< 5 ms) where the shell startup overhead correction would
 produce a significant amount of noise. Note that you cannot use shell syntax like `*` or `~` in this case.
 ```
-hyperfine -N 'grep TODO /home/user'
+hyperfine -N 'grep -R TODO /home/user'
 ```