Proposal to include license information via #172. (#175)

Note that I am NOT the copyright owner or have any affiliation with the
piwik project.  This commit and the resulting PR were made informed by
aforementioned issue (#172) and the fact that the 'main' piwik git
repository includes this very repository and does not state
licence/copyright/trademark exceptions.  This commit is a pure proposal.

LEGALNOTICE

@@ -0,0 +1,26 @@
+COPYRIGHT
+
+  Piwik - free/libre analytics platform
+
+  The software package is:
+
+    Copyright (C) 2014  Matthieu Aubry
+
+  Individual contributions, components, and libraries are copyright
+  of their respective authors.
+
+
+SOFTWARE LICENSE
+
+  The free software license of Piwik is GNU General Public License v3
+  or later.  A copy of GNU GPL v3 should have been included in this
+  software package in LICENCE.txt.
+
+
+TRADEMARK
+
+  Piwik (TM) is an internationally registered trademark.
+
+  The software license does not grant any rights under trademark
+  law for use of the trademark.  Refer to http://piwik.org/trademark/
+  for up-to-date trademark licensing information.