Added license to README

Author: cliffordwolf

README

@@ -2,3 +2,17 @@ Project IceStorm aims at documenting the bitstream format of Lattice iCE40
 FPGAs and providing simple tools for analyzing and creating bitstream files.
 
 See http://www.clifford.at/icestorm/ for more information.
+
+Most of Project IceStorm is licensed under the ISC license:
+
+#  Permission to use, copy, modify, and/or distribute this software for any
+#  purpose with or without fee is hereby granted, provided that the above
+#  copyright notice and this permission notice appear in all copies.
+#
+#  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+#  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+#  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+#  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+#  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+#  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+#  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.