Add X11 license file

LICENSE.md

@@ -0,0 +1,24 @@
+ObjSim is licensed under the MIT/X11:
+
+    Copyright (C) 2005 - 2020 Frank Michler, Sebastian Thomas Philipp
+    
+    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 X CONSORTIUM 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.
+    
+The MIT/X11 is a permissive license, which is GPL compatible, 
+and allows usage within proprietary software as long as this license 
+is distributed along with the software.