Update signup link

Author: Adamj1232

packages/react/README.md

@@ -28,7 +28,7 @@ import torusModule from '@web3-onboard/torus'
 import keepkeyModule from '@web3-onboard/keepkey'
 import dcentModule from '@web3-onboard/dcent'
 
-// Sign up to get your free API key at https://www.blocknative.com/pricing
+// Sign up to get your free API key at https://explorer.blocknative.com/?signup=true
 const dappId = '1730eff0-9d50-4382-a3fe-89f0d34a2070'
 
 const injected = injectedModule()