added comment for user clarity (#5724)

libraries/WebServer/examples/SDWebServer/SDWebServer.ino

@@ -25,6 +25,8 @@
   index.htm is the default index (works on subfolders as well)
 
   upload the contents of SdRoot to the root of the SDcard and access the editor by going to http://esp8266sd.local/edit
+  To retrieve the contents of SDcard, visit http://esp32sd.local/list?dir=/
+      dir is the argument that needs to be passed to the function PrintDirectory via HTTP Get request.
 
 */
 #include <WiFi.h>