Explain why StepInfo's assignment operator is deleted

Because I've seen this code to often, wondering why I shouldn't just
delete this line. Turns out it is because of PR #128 which fixes #127.

Author: muggenhor

include/cucumber-cpp/internal/step/StepManager.hpp

@@ -104,8 +104,8 @@ class StepInfo : public boost::enable_shared_from_this<StepInfo> {
     Regex regex;
     const std::string source;
 private:
+    // Shut up MSVC warning C4512: assignment operator could not be generated
     StepInfo& operator=(const StepInfo& other);
-    
 };