docs: add a hint about making ^L do just 'refresh' to the sample nanorc

Just for the sake of completeness -- I doubt anyone ever uses Refresh.

doc/sample.nanorc.in

@@ -265,6 +265,9 @@
 ## <Ctrl+Backspace> delete the word to the left of the cursor with:
 # bind ^H chopwordleft main
 
+## If you want ^L to just refresh the screen and not center the cursor:
+# bind ^L refresh main
+
 ## For quickly uppercasing or lowercasing the word under the cursor.
 ## (These effectively do a Ctrl+Right followed by a Shift+Ctrl+Left,
 ## and then pipe the selected text through a sed command.)