docs: add Surely to Used By (#1094)

Author: CodingItWrong

versioned_docs/version-6.x/used-by.md

@@ -44,6 +44,7 @@ It's impossible to list every single app that uses React Navigation, but below a
 - [Skeel](https://www.skeelapp.com/) ([iOS](https://apps.apple.com/fr/app/skeel-qui-est-le-meilleur/id1292404366)) ([Android](https://play.google.com/store/apps/details?id=com.skeelofficial.reactnativeclient))
 - [Stillwhite: Wedding Dresses](https://www.stillwhite.com/) ([iOS](https://apps.apple.com/us/app/stillwhite-wedding-dresses/id1483180828)) ([Android](https://play.google.com/store/apps/details?id=com.stillwhite.app))
 - [Summer](https://www.summerapp.com/) ([iOS](https://apps.apple.com/app/apple-store/id1512328590?pt=118010433))
+- [Surely Todos](https://www.surelytodo.com/) ([iOS](https://apps.apple.com/us/app/surely/id1586633713)) ([Web](https://www.surelytodo.com/))
 - [Sweepy](https://sweepy.app/)
 - [Tracker Network for Fortnite](https://apps.apple.com/us/app/tracker-network-for-fortnite/id1287696482)
 - [Vrbo](https://www.vrbo.com/mobile/)