[Pagination] - Added props doc mentioning the activePage is zero based

[theodesp]

Summary

Included documentation entry for activePage prop mentioning that the activePage is zero based.
Ref: #1667

Checklist

• This was checked in mobile
• This was checked in IE11
• This was checked in dark mode
• Any props added have proper autodocs
• Documentation examples were added
• A changelog entry exists and is marked appropriately
• This was checked for breaking changes and labeled appropriately
• Jest tests were updated or added to match the most common scenarios
• This was checked against keyboard-only and screenreader scenarios
• This required updates to Framer X components

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[chandlerprall]

jenkins test this

[chandlerprall]

LGTM; built docs locally and verified the change appears as expected

[chandlerprall]

@theodesp can you move the changelog entry to the top of the log? Unfortunately the way we write them, git associates the entries with the above/below lines and your change is now associated with a released version. With that update I'll merge this in!

[theodesp]

@chandlerprall I've moved the entry to the current master

[theodesp]

I have updated my Changelog to reflect the latest changes. Thanx

[thompsongl]

jenkins test this