docs: Update README

Author: ErikSchierboom

exercises/clock/README.md

@@ -9,7 +9,7 @@ Two clocks that represent the same time should be equal to each other.
 ## Hints
 This exercise requires you to implement a type-specific method for determining equality of instances.
 For more information, see [this page]
-(https://docs.microsoft.com/en-us/dotnet/core/api/System.IEquatable-1) .
+(https://docs.microsoft.com/en-us/dotnet/core/api/System.IEquatable-1).
 
 
 ## Running the tests

exercises/leap/README.md

@@ -26,6 +26,11 @@ phenomenon, go watch [this youtube video][video].
 
 [video]: http://www.youtube.com/watch?v=xX96xng7sAE
 
+## Notes
+
+The DateTime class in C# provides a built-in [IsLeapYear](https://msdn.microsoft.com/en-us/library/system.datetime.isleapyear(v=vs.110).aspx) method
+which you should pretend doesn't exist for the purposes of implementing this exercise.
+
 ## Running the tests
 
 To run the tests, run the command `dotnet test` from within the exercise directory.