[webrtc-pc] Pull Request: move rescale paragraph

fippo has just submitted a new pull request for https://github.com/w3c/webrtc-pc:

== move rescale paragraph ==
moves the paragraph that explains cropping to the beginning
of the media api section.

Fixes #1243

just moving stuff, but I actually fixed a dangling whitespace at the end ;-)

See https://github.com/w3c/webrtc-pc/pull/1468