Prepare the 2.8.0.dev1 release. (pantsbuild#12845)

CONTRIBUTORS.md

@@ -137,6 +137,7 @@ Created by running `./build-support/bin/contributors.sh`.
 + Luca Clementi
 + Lukasz Jastrzebski
 + Marc Abramowitz
++ Marcelo Trylesinski
 + Marcin Podolski
 + Marek Żarnowski
 + Marilyn Cruz

src/python/pants/VERSION

@@ -1 +1 @@
-2.8.0.dev0
+2.8.0.dev1

src/python/pants/notes/2.8.x.md

@@ -1,5 +1,51 @@
 # 2.8.x Release Series
 
+## 2.8.0.dev1 (Sep 10, 2021)
+
+### New Features
+
+* Support --fail-under on merged coverage. ([#12778](https://github.com/pantsbuild/pants/pull/12778))
+
+* Add python-docx to the module mapping dictionary ([#12775](https://github.com/pantsbuild/pants/pull/12775))
+
+* Add python-pptx to the module mapping dictionary ([#12776](https://github.com/pantsbuild/pants/pull/12776))
+
+* Add `opencv-python` to the default Python module mapping ([#12777](https://github.com/pantsbuild/pants/pull/12777))
+
+* Add `PyMuPDF` to the default Python module mapping ([#12774](https://github.com/pantsbuild/pants/pull/12774))
+
+### User API Changes
+
+* Deprecate `--list-provides` option. ([#12759](https://github.com/pantsbuild/pants/pull/12759))
+
+* Upgrade default `isort` to latest `isort==5.9.3` ([#12756](https://github.com/pantsbuild/pants/pull/12756))
+
+* Add `version` to lockfile metadata headers ([#12788](https://github.com/pantsbuild/pants/pull/12788))
+
+### Plugin API Changes
+
+* `OutputPathField.value_or_default()` no longer has an `Address` argument ([#12837](https://github.com/pantsbuild/pants/pull/12837))
+
+### Bug fixes
+
+* Properly include file dependencies in docker build context ([#12758](https://github.com/pantsbuild/pants/pull/12758))
+
+* DigestSubset should not short-circuit when there are ignores involved. ([#12648](https://github.com/pantsbuild/pants/pull/12648))
+
+* Fix backports of std lib modules like `dataclasses` not working with dependency inference ([#12818](https://github.com/pantsbuild/pants/pull/12818))
+
+### Performance
+
+* Improve cache reuse for `./pants package` when using a constraints file or lockfile ([#12807](https://github.com/pantsbuild/pants/pull/12807))
+
+* Upgrade to Pex 2.1.48 and leverage packed layout. ([#12808](https://github.com/pantsbuild/pants/pull/12808))
+
+### Documentation
+
+* Warn if `[python-repos]` is set during lockfile generation ([#12800](https://github.com/pantsbuild/pants/pull/12800))
+
+* Fix a markdown issue in a help string. ([#12766](https://github.com/pantsbuild/pants/pull/12766))
+
 ## 2.8.0.dev0 (Sep 03, 2021)
 
 ### New Features