Prepare the 2.9.0.dev1 release. (#13610)

[ci skip-rust]

CONTRIBUTORS.md

@@ -116,6 +116,7 @@ Created by running `./build-support/bin/contributors.sh`.
 + Jonathan Sokolowski
 + Josh Reed
 + Josh Soref
++ Joshua Cannon
 + Joshua Cohen
 + Joshua Humphries
 + Justin Trobec

src/python/pants/VERSION

@@ -1 +1 @@
-2.9.0.dev0
+2.9.0.dev1

src/python/pants/notes/2.9.x.md

@@ -1,5 +1,39 @@
 # 2.9.x Release Series
 
+## 2.9.0.dev1 (Nov 13, 2021)
+
+### New Features
+
+* Add `instructions` field to `docker_image` to support generating the Dockerfile ([#13386](https://github.com/pantsbuild/pants/pull/13386))
+
+* Add `--unowned-dependency-behavior` option for Python ([#13491](https://github.com/pantsbuild/pants/pull/13491))
+
+### User API Changes
+
+* Upgrade default pylint to v2.11.1 ([#13585](https://github.com/pantsbuild/pants/pull/13585))
+
+### Plugin API Changes
+
+* [plugin-api] Add `default_glob_match_error_behavior` to `SourcesField`. ([#13578](https://github.com/pantsbuild/pants/pull/13578))
+
+### Bug fixes
+
+* Fix `--no-print-stacktrace`. ([#13539](https://github.com/pantsbuild/pants/pull/13539))
+
+### Performance
+
+* Do not invalidate parent paths when only file content has changed ([#13566](https://github.com/pantsbuild/pants/pull/13566))
+
+* Fix caching of binary lookups and avoid re-running `pytest` setup for environment changes ([#13559](https://github.com/pantsbuild/pants/pull/13559))
+
+* Fix slow performance from recursive `__repr__` and `__hash__` for Go ([#13492](https://github.com/pantsbuild/pants/pull/13492))
+
+* Go: improve performance of first-party package analysis ([#13476](https://github.com/pantsbuild/pants/pull/13476))
+
+### Documentation
+
+* Fix `tailor` confusion with macros vs. targets ([#13574](https://github.com/pantsbuild/pants/pull/13574))
+
 ## 2.9.0.dev0 (Nov 03, 2021)
 
 ### New Features