Clarify dirs

Signed-off-by: jolheiser <john.olheiser@gmail.com>

README.md

@@ -1,6 +1,8 @@
 # Dynmap JS
 
-Add `canopy.js` to `index.html` like so:
+`$PLUGIN` refers to the dynmap plugin directory
+
+Add [canopy.js](canopy.js) to `$PLUGIN/web/js` and link it in `$PLUGIN/web/index.html` like so:
 
 ```diff
         ...