added Makefile example from flex documentation

Makefile

@@ -0,0 +1,14 @@
+# Basic Makefile example from flex documentation -- provides explicit rules
+# Creates "myprogram" from "scan.l" and "myprogram.c"
+#
+#LEX=flex
+#myprogram: scan.o myprogram.o
+#$(CC) -o $@ $(LDFLAGS) $^
+#myprogram.o: myprogram.c
+#$(CC) $(CPPFLAGS) $(CFLAGS) -o $@ -c $^
+#scan.o: scan.c
+#$(CC) $(CPPFLAGS) $(CFLAGS) -o $@ -c $^
+#scan.c: scan.l
+#$(LEX) $(LFLAGS) -o $@ $^
+#clean:
+#$(RM) *.o scan.c