[css-animations-2] Add Changes section

[SebastianZ]

Probably a little too late for the FPWD but I think there should be a Changes section added like in other specs. This makes it easier to grasp what has changed since level 1 of the spec.

Sebastian

[svgeesus]

Yes, a "Changes since Level 1" would be helpful. That could be done now, because FPWD of CSS Animations 2 is waiting for an update to CSS Animations 1

Once the FPWD has been published, changes since last publication should also be added.

[svgeesus]

I added a "Changes since Level 1" section.

[SebastianZ]

Thanks for adding the section! I've just fixed a typo and linked the properties and interface in there, so it's a little easier to skim through it and get to the described changes.

Sebastian