Add note about anonymous accounts for Alexa tutorials

[ewpatton]

For students using the Alexa system with anonymous accounts, the setup instructions in the tutorials that point to how to set up a developer account are not relevant. We should include a note at the start of that section to the effect of "You can skip this section if you don't see a login button below the testing window." Otherwise, folks might get confused.

[ewpatton]

@stezelMIT @bobparks If we can decide on final language for this, then @eviecaii and @robinl21 can update the tutorials accordingly.

[stezelMIT]

Folks will be arriving at the Designer page of regular App Inventor in these projects first and until they create an Alexa skill they will not be exposed to the testing interface and see if they have a login button or not. So I don't think the suggestion above can work. How about "If your instructor gave you access to an anonymous Alexa account then you can skip this section on how to set up an Alexa Developer Account." ?

[stezelMIT]

@ewpatton I added the comment "If your instructor gave you access to an anonymous Alexa account then you can skip this section on how to set up an Alexa Developer Account." to each of the Alexa projects and did a PR on yrtoolkit site. Kindly review ASAP and let me know if it looks OK.