COPYING: Add the MIT License and add a note about plugins being licensed individually.

COPYING

@@ -1,3 +1,35 @@
+collectd consists of a daemon and numerous plugins. The daemon is licensed
+under the "MIT License"; its source files are located at src/daemon/. The
+plugins are licenses individually, please check the top of the plugin's source
+file(s) to see which license applies. The majority of plugins is licensed
+either under the "MIT License" or the "GNU General Public License".
+
+The "MIT License" and "GNU General Public License" follow. Other licenses, not
+included in this file, should be considered "as published by the Open Source
+Initiative (OSI)".
+
+MIT License
+===========
+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.
+
+GNU General Public License (GPL)
+================================
 		    GNU GENERAL PUBLIC LICENSE
 		       Version 2, June 1991