mostlymatter/web/static/config/manifest.json

{
  "name": "Mattermost",
  "icons": [
    {
      "src": "../static/iamges/icon50x50.png",
      "sizes": "50x50",
      "type": "image/png"
    }
  ],
  "start_url": "/",
  "display": "standalone",
  "orientation": "portrait"
}