Add a proper MIT LICENSE file.

Fixes #122.

LICENSE

@@ -0,0 +1,31 @@
+The MIT License (MIT)
+
+Copyright © 2013 - 2014 Heroku, Keith Rarick and the hk
+contributors. A full list of contributors is available on GitHub:
+
+    https://github.com/heroku/hk/graphs/contributors
+
+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.
+
+For source code, to contribute to hk, or just to say hello:
+
+    https://github.com/heroku/hk
+
+Happy hacking!

about.go

@@ -6,8 +6,10 @@ var helpAbout = &Command{
 	Short:    "information about hk (e.g. copyright, license, etc.)",
 	Long: userAgent + `
 
-Copyright © 2013 Keith Rarick and the hk contributors. A full list of
-contributors is available on GitHub:
+The MIT License (MIT)
+
+Copyright © 2013 - 2014 Heroku, Keith Rarick and the hk
+contributors. A full list of contributors is available on GitHub:
 
     https://github.com/heroku/hk/graphs/contributors