Update Generate_Folder_Tree.md

Signed-off-by: Feldwor <BoQsc@users.noreply.github.com>

Operating_System/System_Tools/Directory_Tree_Generator/Generate_Folder_Tree.md

@@ -60,6 +60,7 @@ Recursively list all the contents of the current folder.
 Ident and use characters to emphasise structure of folders and files.
 
 D Language
+https://dlang.org/phobos/std_file.html#.dirEntries
 ```
 import std;
 void main() {