[TASK][DOC] (issue7_refract): add command to test mode 2

src/ts/refract/testcase/README

@@ -8,4 +8,10 @@ The rules in Makefile expect refmet to be installed. The reflectivity method
 as implemented in refmet is provided in Seitosh in subdirectory
 src/synt/ref/refmet
 
+----------------------------------------------------------------------------
+Test mode 2:
+
+  refract -Sm 2 -v -Sr 0.527 -p -St -0.02,0.12 -Sx 0.,150. \
+    set1.sff set2.sff set3.sff
+
 ----- END OF README -----