Add Playground link to navbar pointing to Hugging Face Spaces (MemMachine#561)

Co-authored-by: Anirudh Esthuri <[email protected]>

Author: Anirudhem-mv

docs/docs.json

@@ -138,6 +138,10 @@
   },
   "navbar": {
     "links": [
+      {
+        "label": "Playground",
+        "href": "https://huggingface.co/spaces/Memverge/MemMachine-Playground"
+      },
       {
         "label": "Support",
         "href": "mailto:[email protected]"