The install docs are now versioned, and I also don't see hardcoded Bazel version numbers in the installation instructions anymore.

https://docs.bazel.build/versions/0.20.0/install-windows.html
https://docs.bazel.build/versions/0.20.0/install-ubuntu.html
Use a variable for latest Bazel version number in docs
Our install docs are often displaying the latest version number to download: http://docs.bazel.build/versions/master/install-ubuntu.html

Today, this is hardcoded in the text.
We should introduce a variable that is defined in one place and that we update when performing the release.
https://github.com/bazelbuild/bazel/blob/master/site/_config.yml is probably the place to put this variable.
scripts/docs/doc_versions.bzl site/_config.yml
scripts/docs/doc_versions.bzl site/_config.yml
diff --git a/scripts/docs/doc_versions.bzl b/scripts/docs/doc_versions.bzl
index 4e4b76a5ffc52e..09f2c80aacfdd9 100644
--- a/scripts/docs/doc_versions.bzl
+++ b/scripts/docs/doc_versions.bzl
@@ -22,6 +22,10 @@
 """This module contains the versions and hashes of Bazel's documentation tarballs."""
 
 DOC_VERSIONS = [
+    {
+        "version": "0.21.0",
+        "sha256": "23ec39c0138d358c544151e5c81586716d5d1c6124f10a742bead70516e6eb93",
+    },
     {
         "version": "0.20.0",
         "sha256": "bb79a63810bf1b0aa1f89bd3bbbeb4a547a30ab9af70c9be656cc6866f4b015b",
diff --git a/site/_config.yml b/site/_config.yml
index 00f82998f49c69..9e82fe02e149d8 100644
--- a/site/_config.yml
+++ b/site/_config.yml
@@ -15,6 +15,7 @@ version: "master"
 # This must be kept in sync with //site/script/docs:versions.bzl
 doc_versions:
   - master
+  - 0.21.0
   - 0.20.0
   - 0.19.2
   - 0.19.1
