Where to find Selenium Webdriver release notes?

They live in the source control for the project under the respective folder for the particular language libraries. That means:

1. .NET Libraries: https://github.com/SeleniumHQ/selenium/blob/master/dotnet/CHANGELOG
2. Java Libraries: https://github.com/SeleniumHQ/selenium/blob/master/java/CHANGELOG
3. Python Libraries: https://github.com/SeleniumHQ/selenium/blob/master/py/CHANGES
4. Ruby libraries: https://github.com/SeleniumHQ/selenium/blob/master/rb/CHANGES
5. NodeJS libraries: https://github.com/SeleniumHQ/selenium/blob/master/javascript/node/selenium-webdriver/CHANGES.md

'Special' ones:

1. IEDriverServer changelog: https://github.com/SeleniumHQ/selenium/blob/master/cpp/iedriverserver/CHANGELOG

1. visit http://docs.seleniumhq.org/
2. Click 'Download' tab.
3. Scroll down to section 'Selenium Client & WebDriver Language Bindings'
4. 'Change log' link for each languages.