Fix branch documentation

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=128707067

CONTRIBUTING.md

@@ -17,8 +17,9 @@ gives some examples of what to include.
 ## Pull requests ##
 
 We will also consider high quality pull requests. These should normally merge
-into the [dev][] branch rather than master. To contribute in this way you must
-first submit a Contributor License Agreement, as described below.
+into the `dev-vX` branch with the highest major version number. Bug fixes may
+be suitable for merging into older `dev-vX` branches. Before a pull request can
+be accepted you must submit a Contributor License Agreement, as described below.
 
 [dev]: https://github.com/google/ExoPlayer/tree/dev
 

README.md

@@ -64,12 +64,15 @@ and copy `library.jar` to the libs folder of your new project.
 
 #### Project branches ####
 
-  * The [`master`][master] branch holds the most recent minor release.
-  * Most development work happens on the [`dev`][dev] branch.
-  * Additional development branches may be established for major features.
-
-[master]: https://github.com/google/ExoPlayer/tree/master
-[dev]: https://github.com/google/ExoPlayer/tree/dev
+  * The project has `dev-vX` and `release-vX` branches, where `X` is the major
+    version number.
+  * Most development work happens on the `dev-vX` branch with the highest major
+    version number. Pull requests should normally be made to this branch.
+  * Bug fixes may be submitted to older `dev-vX` branches. When doing this, the
+    same (or an equivalent) fix should also be submitted to all subsequent
+    `dev-vX` branches.
+  * A `release-vX` branch holds the most recent stable release for major version
+    `X`.
 
 #### Using Android Studio ####