Update deploy-to-testnet.md with chain onboarding note (#461)

* Update deploy-to-testnet.md

* Update tutorials/polkadot-sdk/parachains/zero-to-hero/deploy-to-testnet.md

Co-authored-by: 0xLucca <[email protected]>

---------

Co-authored-by: Nicolás Hussein <[email protected]>
Co-authored-by: 0xLucca <[email protected]>

Author: 3 people

tutorials/polkadot-sdk/parachains/zero-to-hero/deploy-to-testnet.md

@@ -179,6 +179,9 @@ Once you have the genesis state and runtime, you can now register these with you
 
 Your parachain's runtime logic and genesis are now part of the relay chain. The next step is to ensure you are able to run a collator to produce blocks for your parachain.
 
+!!!note 
+    You may need to wait several hours for your parachain to onboard. Until it has onboarded, you will be unable to purchase coretime, and therefore will not be able to perform transactions on your network.
+
 ## Start the Collator Node
 
 Before starting a collator, you need to generate a node key. This key is responsible for communicating with other nodes over Libp2p: