sponsorship: Add consultancies

sponsorship.mkd

@@ -14,6 +14,9 @@ These sponsors should be listed in:
  * [QBayLogic](https://qbaylogic.com/)
  * [Channable](https://www.channable.com/)
  * [Haskell Foundation](https://haskell.foundation/)
+ * [Serokell](https://serokell.io/)
+ * [Well-Typed](https://well-typed.com/)]
+ * [Tweag](https://www.tweag.io/)
  * [Dotcom-Monitor](https://www.dotcom-monitor.com/)
  * [LoadView](https://www.loadview-testing.com/)
  * [Web Hosting Buddy](https://webhostingbuddy.com/)