Add note regarding NCTL status for integration tests

Signed-off-by: David Hernando <[email protected]>

README.md

@@ -68,9 +68,10 @@ The command above excludes integration tests. If you're running a Casper network
 dotnet test --settings Casper.Network.SDK.Test/test.runsettings --filter 'TestCategory~NCTL'
 ```
 
+NOTE: Make sure your NCTL network has booted up and nodes are emitting blocks before running the tests.
+
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