Amend comment to explain what LoadCodepoints is doing. (#4787)

As a beginner, it was not clear to me what the purpose of the LoadCodepoints function is. I am trying to help past me.

examples/text/text_codepoints_loading.c

@@ -38,7 +38,8 @@ int main(void)
 
     InitWindow(screenWidth, screenHeight, "raylib [text] example - codepoints loading");
 
-    // Get codepoints from text
+    // Convert each utf-8 character into its
+    // corresponding codepoint in the font file.
     int codepointCount = 0;
     int *codepoints = LoadCodepoints(text, &codepointCount);