Update release doc to include testnet update instuctions (#4066)

* Update release doc to include testnet update instuctions

* Fixup headers and pick nits

* Remove outdated testnet behavior

RELEASE.md

@@ -61,7 +61,7 @@ There are three release channels that map to branches as follows:
 
 ## Release Steps
 
-### Changing channels
+### Advance the Channels
 
 #### Create the new branch
 1. Pick your branch point for release on master.
@@ -84,7 +84,7 @@ There are three release channels that map to branches as follows:
 At this point, `ci/channel-info.sh` should show your freshly cut release branch as
 "BETA_CHANNEL" and the previous release branch as "STABLE_CHANNEL".
 
-### Updating channels (i.e. "making a release")
+### Make the Release
 
 We use [github's Releases UI](https://github.com/solana-labs/solana/releases) for tagging a release.
 
@@ -99,13 +99,59 @@ We use [github's Releases UI](https://github.com/solana-labs/solana/releases) fo
    release should be `<branchname>.X-rc.0`.
 1. Verify release automation:
    1. [Crates.io](https://crates.io/crates/solana) should have an updated Solana version.
-   1. ...
-1. After testnet deployment, verify that testnets are running correct software.
-   http://metrics.solana.com should show testnet running on a hash from your
-   newly created branch.
 1. Once the release has been made, update Cargo.toml on the release branch to the next
    semantic version (e.g. 0.9.0 -> 0.9.1) by running
    `./scripts/increment-cargo-version.sh patch`, then rebuild with `cargo
    build` to cause a refresh of `Cargo.lock`.
 1. Push your Cargo.toml change and the autogenerated Cargo.lock changes to the
    release branch.
+
+### Update software on testnet.solana.com
+
+The testnet running on testnet.solana.com is set to use a fixed release tag
+which is set in the Buildkite testnet-management pipeline.
+This tag needs to be updated and the testnet restarted after a new release
+tag is created.
+
+#### Update testnet schedules
+
+Go to https://buildkite.com/solana-labs and click through: Pipelines ->
+testnet-management -> Pipeline Settings -> Schedules
+Or just click here:
+https://buildkite.com/solana-labs/testnet-management/settings/schedules
+
+There are two scheduled jobs for testnet: a daily restart and an hourly sanity-or-restart. \
+https://buildkite.com/solana-labs/testnet-management/settings/schedules/0efd7856-7143-4713-8817-47e6bdb05387
+https://buildkite.com/solana-labs/testnet-management/settings/schedules/2a926646-d972-42b5-aeb9-bb6759592a53
+
+On each schedule:
+1.  Set TESTNET_TAG environment variable to the desired release tag.
+    1. Example, TESTNET_TAG=v0.13.2
+1.  Set the Build Branch to the branch that TESTNET_TAG is from.
+    1. Example: v0.13
+
+#### Restart the testnet
+
+Trigger a TESTNET_OP=create-and-start to refresh the cluster with the new version
+
+1.  Go to https://buildkite.com/solana-labs/testnet-management
+2.  Click "New Build" and use the following settings, then click "Create Build"
+    1.  Commit: HEAD
+    1.  Branch: [channel branch as set in the schedules]
+    1.  Environment Variables:
+```
+TESTNET=testnet
+TESTNET_TAG=[same value as used in TESTNET_TAG in the schedules]
+TESTNET_OP=create-and-start
+```
+
+#### Update documentation
+
+Document the new recommended version by updating
+```export SOLANA_RELEASE=[new scheduled TESTNET_TAG value]```
+in book/src/testnet-participation.md for both edge and beta channel branches.
+
+### Alert the community
+
+Notify Discord users on #validator-support that a new release for
+testnet.solana.com is available