add a test for the find script on the build directory

test/find-package-test/main.cpp

@@ -0,0 +1,8 @@
+#include <cppformat/format.h>
+
+int main(int argc, char** argv)
+{
+  for(int i = 0; i < argc; ++i)
+    fmt::print("{}: {}\n", i, argv[i]);
+  return 0;
+}