Mention the trademark policy in downloaded archive's LICENCE.txt

[林博仁(Buo-ren, Lin)]

As title, currently it only mentions CC BY-SA 3.0, it should mention your trademark policy as well

Example:

```
Delivered by Canonical and friends for web

Copyright 2015 Canonical Ltd.
This work is licensed under the Creative Commons Attribution-Share Alike 3.0
Unported License. To view a copy of this license, visit
http://creativecommons.org/licenses/by-sa/3.0/ or send a letter to Creative
Commons, 171 Second Street, Suite 300, San Francisco, California, 94105, USA.
```

[Inayaili de León (yaili)]

Just a quick update on this bug:

I've updated some of the zips to include an updated LICENSE.txt. There are still a few that need to be updated, but they also have to be updated to include the new Ubuntu Orange, so I will leave this until I can do both changes at once. The files that still need updated license are:

- Ubuntu logo set for web (SVG)
- Ubuntu logo set for web (JPEG)
- Ubuntu logo set for web (PNG)
- Ubuntu Circle of Friends set for web
- Ubuntu Circle of Friends set for print
- Ubuntu logo set for print (CMYK)
- Ubuntu logo set for print (PANTONE)
- Juju logo set
- Ubuntu Core logo set

[Inayaili de León (yaili)]

I've just finished uploading all the remaining files.