Add trademark guidance to UX writing guide.

[edonehoo]

Update UX writing guide to add relevant guidance for using other companies terms/trademarked phrases. Pull whatever from here is actually relevant for PF:

"It is ok to use our competitors trademarks so long as:
It is used accurately to describe the other party’s own goods and
services, and all of the following conditions are met:

• It is not misleading;
• It compares goods or services meeting the same needs or intended
  for the same purpose;
• It objectively compares one or more material, relevant, verifiable
  and representative features of those goods or services,
• It does not create confusion in the marketplace between Red Hat and
  a VMWare;
• It does not discredit or denigrate the trademarks, trade names or
  other distinguishing signs of a competitor;
• It does not take unfair advantage of the trademark or other
  distinguishing sign of a competitor; and
• It does not present goods or services as imitations or replicas of
  goods or services bearing a trademark.
  We may not use a competitor’s trademark as an attention-getting device. We
  should use them in the body text only and avoid using them in headlines,
  titles, and graphics. We always need permission to use a third party's
  logo."