Fix small error

[asorini]

The Hello World guide seems to have a error (or potentially misleading statement) in its description of an expectation value. While it is true that the referenced expectation value is 1 for the specific entangled state created by the example circuit, that expectation value does not have to be 1 for all entangled states.

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[abbycross]

Thank you @asorini ! We need you to sign the CLA before we can merge this PR, if you don't mind doing so?

[asorini]

Hi. Thanks for letting me know. I think I did it, but it doesn't seem to be showing up yet.