Suggest disabled binding on Todo tutorial

[3cp]

Hi @EisenbergEffect, when you redo the todo tutorial, how about add a disabled binding to the button?

<button type="submit" disabled.bind="!todoDescription">Add Todo</button>

[avrahamcool]

I think this issue can be closed, based on the codesandbox on the aurelia.io main page.

[3cp]

I added that in codesandbox, but the tutorial has to be updated. @EisenbergEffect planed to rewrite the tutorial using codesandbox setup.