Update transitions.md

[zakingslayerv22]

Before reading the MDN article - https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_transitions/Using_CSS_transitions as attached in the assignments, I spent a lot of time trying to figure out how the brower automatically knows that it should trigger the transition on hover.

I think informing the readers that transition works with CSS property values that change, can be more helpful and better prepare them for MDN.

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Closes #XXXXX

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