Update Notify section on the docs site and within readme (#1612)

* Update notify docs on docs site and within readme

* Update notify api docs

* Add screenshots

* Update signup link

* Remove export from types in docs

Author: Adamj1232

assets/notify-custom-example.png

@@ -1,6 +1,6 @@
 {
   "name": "@web3-onboard/core",
-  "version": "2.16.0",
+  "version": "2.16.1-alpha.1",
   "description": "Web3-Onboard makes it simple to connect Ethereum hardware and software wallets to your dapp. Features standardized spec compliant web3 providers for all supported wallets, framework agnostic modern javascript UI with code splitting, CSS customization, multi-chain and multi-account support, reactive wallet state subscriptions and real-time transaction state change notifications.",
   "keywords": [
     "Ethereum",