[enh] manifest: add small icon

www/manifest.json

@@ -6,6 +6,11 @@
   "default_locale": "fr",
   "description": "Manage your Duniter Wallet on a libre currency, like Ğ1",
   "icons": [
+    {
+      "src": "img/logo_32px.png",
+      "sizes": "32x32",
+      "type": "image/png"
+    },
     {
       "src": "img/logo_96px.png",
       "sizes": "96x96",