Make comments on example clearer

I actually struggled because I overlooked the fact that I needed to change the 2.1 to "A+". 

So I wanted to make things clearer for future rustlings.

exercises/generics/generics3.rs

@@ -4,8 +4,11 @@
 // However, the school also issues alphabetical grades (A+ -> F-) and needs
 // to be able to print both types of report card!
 
-// Make the necessary code changes to support alphabetical report cards, thereby making
-// the second test pass.
+// Make the necessary code changes in the struct ReportCard and the impl block 
+// to support alphabetical report cards. Change the Grade in the second test to "A+" 
+// to show that your changes allow alphabetical grades.
+
+// Execute 'rustlings hint generics3' for hints!
 
 // I AM NOT DONE