Prepare 2.6.0rc0. (pantsbuild#12259)

CONTRIBUTORS.md

@@ -30,6 +30,7 @@ Created by running `./build-support/bin/contributors.sh`.
 + Chris Livingston
 + Chris Pesto
 + Christopher Livingston
++ Christopher Neugebauer
 + Cody Gibb
 + Craig Schertz
 + Cristian Matache
@@ -138,6 +139,7 @@ Created by running `./build-support/bin/contributors.sh`.
 + Mark Chu-Carroll
 + Mark Davis
 + Mark McBride
++ Martim Lobao
 + Mateo Rodriguez
 + Mathew Jennings
 + Mathieu Sabourin

src/python/pants/VERSION

@@ -1 +1 @@
-2.6.0.dev2
+2.6.0rc0

src/python/pants/notes/2.6.x.md

@@ -1,5 +1,37 @@
 # 2.6.x Stable Releases
 
+## 2.6.0rc0 (Jun 30, 2021)
+
+### New Features
+
+* Add dependency inference for Python third-party type stubs ([#12248](https://github.com/pantsbuild/pants/pull/12248))
+
+* Add `poetry_requirements` macro for Poetry support ([#12174](https://github.com/pantsbuild/pants/pull/12174))
+
+### User API Changes
+
+* Update default MyPy to 0.910 ([#12249](https://github.com/pantsbuild/pants/pull/12249))
+
+* Update linter versions for `pylint`, `black`, `bandit` ([#12135](https://github.com/pantsbuild/pants/pull/12135))
+
+* Upgrade Go distribution to v1.16.5 ([#12247](https://github.com/pantsbuild/pants/pull/12247))
+
+### Plugin API Changes
+
+* Set default user-agent header on gRPC requests with Pants version ([#12241](https://github.com/pantsbuild/pants/pull/12241))
+
+* Increment counter on missing file digests ([#12235](https://github.com/pantsbuild/pants/pull/12235))
+
+### Bug fixes
+
+* Add support for multiple requirements for a single package name in the `python_requirements` macro ([#12232](https://github.com/pantsbuild/pants/pull/12232))
+
+* Fix dependency inference to be ambiguous when >1 type stub for same module ([#12244](https://github.com/pantsbuild/pants/pull/12244))
+
+* Hash the `repo_id` in the tag. ([#12151](https://github.com/pantsbuild/pants/pull/12151))
+
+* Fix `skip_tool` not working with `./pants fmt` if all files are skipped ([#12230](https://github.com/pantsbuild/pants/pull/12230))
+
 ## 2.6.0.dev2 (Jun 16, 2021)
 
 ### New Features