Update introduction.md to dict methods views examples

keys(), values(), items() can be recalculated. Assigning to a variable beforehand makes the dynamic attribute of the views clear.
This is my first contribution and very first pull request.

Hi @oezg :wave:

Thank you for taking the time to submit a PR. Unfortunately, I think assigning a variable to palette_I.keys() confuses things here. Especially with the section that follows.

I would rather leave the introduction as it stands for now, and maybe revisit it down the road if it appears to be confusing students.

Hi Bethany,
Thank you for responding so quickly.