add COPYING

This basically follows the licensing terms of the main dbus-python
sources

COPYING

@@ -0,0 +1,28 @@
+As of version 0.82.4, dbus-python itself is released under the following
+permissive non-copyleft license (the same one that was proposed for
+D-Bus core but wasn't achieved):
+
+	Permission is hereby granted, free of charge, to any person
+	obtaining a copy of this software and associated documentation
+	files (the "Software"), to deal in the Software without
+	restriction, including without limitation the rights to use, copy,
+	modify, merge, publish, distribute, sublicense, and/or sell copies
+	of the Software, and to permit persons to whom the Software is
+	furnished to do so, subject to the following conditions:
+
+	The above copyright notice and this permission notice shall be
+	included in all copies or substantial portions of the Software.
+
+	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+	EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+	MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+	NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+	HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+	WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+	OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+	DEALINGS IN THE SOFTWARE.
+
+Copyright holders and licensing are indicated in the source files.
+
+The dbus-gmain/ subdirectory is under a different license: see
+dbus-gmain/COPYING for details.