Prepare 2.6.0rc1 (pantsbuild#12265)

[ci skip-rust]

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

@@ -1,5 +1,27 @@
 # 2.6.x Stable Releases
 
+## 2.6.0rc1 (Jul 7, 2021)
+
+### New Features
+
+* Add support for MyPy report files (Cherry-pick of #12271) ([#12289](https://github.com/pantsbuild/pants/pull/12289))
+
+### Bug fixes
+
+* Hotfix `poetry_requirements` not being recognized as a macro in BUILD files (Cherry-pick of #12263) ([#12264](https://github.com/pantsbuild/pants/pull/12264))
+
+* Do not use `[python-setup].resolve_all_constraints` when using `platforms` (Cherry-pick of #12268) ([#12269](https://github.com/pantsbuild/pants/pull/12269))
+
+* Fix poetry_requirements: ignore internal projects. (Cherry-pick of #12280) ([#12296](https://github.com/pantsbuild/pants/pull/12296))
+
+* Fix poetry_requirements handling of python. (#12278) ([#12282](https://github.com/pantsbuild/pants/pull/12282))
+
+* Include experimental Go backends in pantsbuild.pants (Cherry-pick of #12290) ([#12291](https://github.com/pantsbuild/pants/pull/12291))
+
+### Documentation
+
+* Change how we embed docsite links in help text (Cherry-pick of #12261) ([#12266](https://github.com/pantsbuild/pants/pull/12266))
+
 ## 2.6.0rc0 (Jun 30, 2021)
 
 ### New Features