installation: copy files AUTHORS COPYING.LGPL README into prefix directory when installing StarPU

Makefile.am

@@ -42,3 +42,9 @@ include_HEADERS = 				\
 	include/starpu_profiling.h		\
 	include/starpu_bound.h			\
 	include/starpu_scheduler.h
+
+txtdir = ${prefix}
+txt_DATA = AUTHORS COPYING.LGPL README
+
+
+