add Acknowledgement section

Author: ko1

README.md

@@ -478,3 +478,7 @@ NOTE
 Bug reports and pull requests are welcome on GitHub at https://github.com/ruby/debug.
 
 Please also check the [contributing guideline](/CONTRIBUTING.md).
+
+# Acknowledgement
+
+* Some tests are based on [deivid-rodriguez/byebug: Debugging in Ruby 2](https://github.com/deivid-rodriguez/byebug)

misc/README.md.erb

@@ -327,3 +327,7 @@ The `<...>` notation means the argument.
 Bug reports and pull requests are welcome on GitHub at https://github.com/ruby/debug.
 
 Please also check the [contributing guideline](/CONTRIBUTING.md).
+
+# Acknowledgement
+
+* Some tests are based on [deivid-rodriguez/byebug: Debugging in Ruby 2](https://github.com/deivid-rodriguez/byebug)