Adding license info to README.

README

@@ -87,4 +87,12 @@ supported:
   * Unified Context Diff
   * Cascading Style Sheets (CSS)
   * Extensible Markup Language (XML)
-  * (Extensible) HyperText Markup Language ((X)HTML)
+  * (Extensible) HyperText Markup Language ((X)HTML)
+
+License
+============================
+
+highlight is released under the unlicense license. See the LICENSE
+file for the complete license and <http://unlicense.org/> for more
+info. In summary, you can do whatever you want with highlight
+including re-licensing.