Update the favicon

I took the SVG favicon from the brand assets pack Creative Coop
produced and put it through an online tool[1] to
generate these files.

[1] https://realfavicongenerator.net

assets/img/site.webmanifest

@@ -0,0 +1,21 @@
+{
+  "name": "CoTech",
+  "short_name": "CoTech",
+  "icons": [
+    {
+      "src": "/web-app-manifest-192x192.png",
+      "sizes": "192x192",
+      "type": "image/png",
+      "purpose": "maskable"
+    },
+    {
+      "src": "/web-app-manifest-512x512.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "maskable"
+    }
+  ],
+  "theme_color": "#ffffff",
+  "background_color": "#ffffff",
+  "display": "standalone"
+}