Added item for Studio URL changes to Release Notes

@JAAkana @srpearce 
I might suggest using either one of our own links, or using an abstract example. People occasionally ask how they can get nice names for their units and subsections, and it's hard to explain that semantic naming come from xml courses.
 
Either:
https://studio.edx.org/unit/location:ORG+COURSE+RUN+vertical+19a30717eff543078a5d94ae9d6c18a5

or something from the demo course. Although a quick check of the demo course shows that it's got lots of xml naming as well!