doc: add more lts update steps to release guide

This changeset adds references to two steps required for promoting a
release line to LTS:

- Adding the new codename to nodejs-latest-linker repo
- Adding codename info to the Release repo

Signed-off-by: Ruy Adorno <ruyadorno@google.com>

doc/contributing/releases.md

@@ -1034,6 +1034,24 @@ existing labels for that release line, such as `vN.x`.
 If the release is transitioning from Active LTS to Maintenance, the
 `backport-requested-vN.x` label must be deleted.
 
+### Add new codename to nodejs-latest-linker
+
+In order to make sure a download URL
+(e.g: https://nodejs.org/download/release/latest-codename/) will be available
+for the new LTS release line you need to submit a PR to
+https://github.com/nodejs/nodejs-latest-linker and add a new entry for the new
+LTS codename in its `ltsNames` map located in the `./latest-linker.js` file.
+
+Make sure to reach out to the Build WG in order to validate that the new URL is
+available as part of the LTS release promotion.
+
+### Update Release repo info
+
+Add the new LTS codename to the release schedule table located in the
+`./README.md` file located at the https://github.com/nodejs/Release repository
+along with the addition of the new codename to the `./schedule.json` file in
+that same repo.
+
 ## Major releases
 
 The process for cutting a new Node.js major release has a number of differences