Add NOTICE file

Add a NOTICE file containing some information about the project.

Signed-off-by: Michael Munday <mike.munday@lowrisc.org>

NOTICE

@@ -0,0 +1,10 @@
+The Ibex project
+Copyright 2024 lowRISC contributors.
+
+This product includes hardware and/or software developed as part of the Ibex®
+(https://github.com/lowRISC/ibex) and OpenTitan® projects.
+
+Ibex was originally developed by the PULP team at ETH Zürich and University of
+Bologna under the name zero-riscy. Ibex verification, performance enhancement
+and security hardening have been supported by the OpenTitan project
+(https://www.opentitan.org).