fix 1988/spinellis

Prevent the Makefile from hanging on stdin by
providing some sample input files and asking the
user to run the command themselves.

1988/spinellis/input2.txt

@@ -0,0 +1,11 @@
+#include <stdio.h>
+
+int
+main(void)
+{
+    int i;
+    for (i = 0; i < 5; ++i) {
+	printf("%d\n", i);
+    }
+    return 0;
+}