Update extensions.json: added Todo Tree (#1283)

- Function: Shows TODO, FIXME, etc. comment tags in a tree view
- Goal: to better manage and track of remaining work

https://marketplace.visualstudio.com/items?itemName=Gruntfuggly.todo-tree

.vscode/extensions.json

@@ -10,5 +10,6 @@
         "will-stone.in-any-case",
         "EditorConfig.editorconfig",
         "PKief.material-icon-theme",
+        "Gruntfuggly.todo-tree"
     ]
 }