clarified extraneous files

test.cpp

@@ -3,6 +3,7 @@
 #include "libpng_wrapper.hpp"
 using namespace std;
 
+//I was required to write a test function as part of the project; here I test libpng.
 void test_png() {
   png test_image("test_png.png", 500, 500);
   uint32_t w = test_image.width();

test.hpp

@@ -1,6 +1,7 @@
 #ifndef TEST_H
 #define TEST_H
 
+//I was required to write a test function as part of the project; here I test libpng.
 void test_png();
 
 #endif