Document -o cinterop option

#KT-27881 Fixed

Interop/StubGenerator/src/main/kotlin/org/jetbrains/kotlin/native/interop/gen/jvm/main.kt

@@ -93,6 +93,7 @@ Following flags are supported:
   -shims <boolean> adds generation of shims tracing native library calls
   -pkg <fully qualified package name> place the resulting definitions into the package
   -h <file>.h header files to parse
+  -o <file>.klib specifies the resulting library file
 """)
 }