Change "Update" button to "Preview"

[arnoesterhuizen]

...to help guide users to press the "Save & Publish" at the top of the
customizer.

If accepted, I can also change the help text to reflect the renaming of the button.

[westonruter]

@arnoesterhuizen thanks for the PR. I think we actually had it say Preview before. However, a Preview button is actually misleading because it makes it seem like clicking it is optional. However, if you don't click the button then the setting will never be updated and their changes will not be saved. So I think something more forceful is needed.

[arnoesterhuizen]

Maybe using "Apply"? I guess this would need more user testing.

Feel free to delete the pull request if this isn't viable right now.

[westonruter]

@shaunandrews what do you think? Is "Apply" better than "Update"?

[shaunandrews]

I like Apply.

[westonruter]

@arnoesterhuizen you can go ahead and change it to using "Apply". How would you change the help text?

[arnoesterhuizen]

Just changing the text in the readme files to refer to the "Apply" button. The screenshots I won't be able to help with necessarily, but I can try.

[westonruter]

Thanks! Merged into develop.