[Keyboard] move ymd96 to ymdk vendor folder (#15643)

keyboards/ymdk/ymd96/readme.md

@@ -8,11 +8,11 @@ A 96-keyboard which supports both ANSI and ISO along with many different layout
 
 Make example for this keyboard (after setting up your build environment):
 
-    make ymd96:default
+    make ymdk/ymd96:default
 
 Flashing example for this keyboard ([after setting up the bootloadHID flashing environment](https://docs.qmk.fm/#/flashing_bootloadhid))
 
-    make ymd96:default:flash
+    make ymdk/ymd96:default:flash
 
 **Reset Key**: Hold down the key commonly programmed as *L_Ctrl* while plugging in the keyboard.