add copyright file.

debian/copyright

@@ -0,0 +1,27 @@
+This work was packaged for Debian by:
+
+    Kouhei Sutou <kou@clear-code.com> on Thu, 02 Sep 2010 13:51:56 +0900.
+
+It was downloaded:
+
+    <http://github.com/mroonga/mroonga/downloads>
+
+Upstream Author(s):
+
+    Tetsuro IKEDA <ikdttr at gmail.com>
+    Daijiro MORI <morita at razil. jp>
+    Tasuku SUENAGA <a at razil. jp>
+    Kouhei Sutou <kou at clear-code. com>
+
+Copyright:
+
+    Copyright(C) 2009-2010 Tetsuro IKEDA
+
+License:
+
+    BSD
+
+    See `/usr/share/common-licenses/BSD'.
+
+The Debian packaging is done by Kouhei Sutou <kou@clear-code.com> in 2010,
+and put into public domain, anyone can use it for any purpose.