Surface links to Stability Policy (GH-2848)

Author: sco1

CHANGES.md

@@ -49,7 +49,8 @@
 ## 22.1.0
 
 At long last, _Black_ is no longer a beta product! This is the first non-beta release
-and the first release covered by our new stability policy.
+and the first release covered by our new
+[stability policy](https://black.readthedocs.io/en/stable/the_black_code_style/index.html#stability-policy).
 
 ### Highlights
 

README.md

@@ -89,6 +89,10 @@ also documented. They're both worth taking a look:
 - [The _Black_ Code Style: Current style](https://black.readthedocs.io/en/stable/the_black_code_style/current_style.html)
 - [The _Black_ Code Style: Future style](https://black.readthedocs.io/en/stable/the_black_code_style/future_style.html)
 
+Changes to the _Black_ code style are bound by the Stability Policy:
+
+- [The _Black_ Code Style: Stability Policy](https://black.readthedocs.io/en/stable/the_black_code_style/index.html#stability-policy)
+
 Please refer to this document before submitting an issue. What seems like a bug might be
 intended behaviour.