doc: document release types in readme

PR-URL: #3482
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

README.md

@@ -13,26 +13,58 @@ We intend to land, with increasing regularity, releases which are
 compatible with the npm ecosystem that has been built to date for
 Node.js.
 
+## Release Types
+
+The Node.js project maintains multiple types of releases:
+
+* **Stable**: Released from active development branches of this repository,
+  versioned by [SemVer](http://semver.org/) and signed by a member of the
+  [Release Team](#release-team).
+  Code for Stable releases is organized in this repository by major version
+  number, For example: [v4.x](https://github.com/nodejs/node/tree/v4.x).
+  The major version number of Stable releases will increment every 6 months
+  allowing for breaking changes to be introduced. This happens in April and
+  October every year. Stable release lines beginning in October each year have
+  a maximum support life of 8 months. Stable release lines beginning in April
+  each year will convert to LTS (see below) after 6 months and receive further
+  support for 30 months.
+* **LTS**: Releases that receive Long-term Support, with a focus on stability
+  and security. Every second Stable release line (major version) will become an
+  LTS line and receive 18 months of _Active LTS_ support and a further 12
+  months of _Maintenance_. LTS release lines are given alphabetically
+  ordered codenames, begining with v4 Argon. LTS releases are less frequent
+  and will attempt to maintain consistent major and minor version numbers,
+  only incrementing patch version numbers. There are no breaking changes or
+  feature additions, except in some special circumstances. More information
+  can be found in the [LTS README](https://github.com/nodejs/LTS/).
+* **Nightly**: Versions of code in this repository on the current Stable
+  branch, automatically built every 24-hours where changes exist. Use with
+  caution.
+
 ## Download
 
 Binaries, installers, and source tarballs are available at
 <https://nodejs.org>.
 
-**Releases** are available at <https://nodejs.org/dist/>, listed under
-their version string. The <https://nodejs.org/dist/latest/> symlink
-will point to the latest release directory.
+**Stable** and **LTS** releases are available at
+<https://nodejs.org/download/release/>, listed under their version strings.
+The [latest](https://nodejs.org/download/release/latest/) directory is an
+alias for the latest Stable release. The latest LTS release from an LTS
+line is available in the form: latest-lts-_codename_. For example:
+<https://nodejs.org/download/release/latest-lts-argon>
 
 **Nightly** builds are available at
 <https://nodejs.org/download/nightly/>, listed under their version
 string which includes their date (in UTC time) and the commit SHA at
 the HEAD of the release.
 
 **API documentation** is available in each release and nightly
-directory under _docs_. <https://nodejs.org/api/> points to the latest version.
+directory under _docs_. <https://nodejs.org/api/> points to the API
+documentation of the latest stable version.
 
 ### Verifying Binaries
 
-Release and nightly download directories all contain a *SHASUM256.txt*
+Stable, LTS and Nightly download directories all contain a *SHASUM256.txt*
 file that lists the SHA checksums for each file available for
 download. To check that a downloaded file matches the checksum, run
 it through `sha256sum` with a command such as:
@@ -44,9 +76,9 @@ $ grep node-vx.y.z.tar.gz SHASUMS256.txt | sha256sum -c -
 _(Where "node-vx.y.z.tar.gz" is the name of the file you have
 downloaded)_
 
-Additionally, releases (not nightlies) have GPG signed copies of
-SHASUM256.txt files available as SHASUM256.txt.asc. You can use `gpg`
-to verify that the file has not been tampered with.
+Additionally, Stable and LTS releases (not Nightlies) have GPG signed
+copies of SHASUM256.txt files available as SHASUM256.txt.asc. You can use
+`gpg` to verify that the file has not been tampered with.
 
 To verify a SHASUM256.txt.asc, you will first need to import all of
 the GPG keys of individuals authorized to create releases. They are