Update README to reflect YUI's updated branching strategy.

README.md

@@ -22,13 +22,36 @@ Source Info
 -----------
 
 This is the active working source tree for YUI 3. It contains work in progress
-toward the next YUI 3 release and may be unstable.
+toward the next YUI 3 releases and may be unstable.
 
 We encourage you to use the latest source for evaluation purposes, testing new
 features and bug fixes, and to provide feedback on new functionality. Please
 refer to the "Latest Production Release" link above if you're looking for the
 latest stable release of YUI recommended for production use.
 
+### Branches
+
+YUI's development happens on three main branches. The following describes what
+each of these code branches represents:
+
+  * `live-docs`: Represents the latest release of YUI, plus any
+    documentation-only updates. Any tweaks or additions to the docs for the
+    latest release happen on this branch, and they are reflected on the website.
+
+  * `master`: Contains everything in `live-docs`, plus code changes that will go
+    into the next YUI release. The code changes in `master` are either bug fixes
+    or small changes which should not break API compatibility. Patch releases
+    will be cut from this branch; e.g. 3.6.x.
+
+  * `3.x`: Represents the next major YUI release; e.g. 3.7.0. This is an
+    integration branch which contains everything in `master`, plus larger code
+    changes which will go into a future YUI release. The changes in `3.x`
+    require a minor version increment before they are part of release; e.g.
+    3.7.0. Preview Releases will be cut from this branch for developers to test
+    and evaluate.
+
+### Source Tree
+
 The YUI source tree includes the following directories:
 
   * `build`: Built YUI source files. The built files are generated at