.sync/Version.njk: Update linux_build_container to for 1.84.0 rust toolchain. (#422)

Update Readme.rst to contain details on process for updating
rust_toolchain.

---------

Co-authored-by: Michael Kubacki <michael.kubacki@microsoft.com>

Author: apop5

.sync/Version.njk

@@ -37,7 +37,7 @@
 {% set previous_mu_release_branch = "release/202311" %}
 
 {# The version of the ubuntu-24-build container to use. #}
-{% set linux_build_container = "ghcr.io/microsoft/mu_devops/ubuntu-24-build:d412ccd" %}
+{% set linux_build_container = "ghcr.io/microsoft/mu_devops/ubuntu-24-build:b089181" %}
 
 {# The Python version to use. #}
 {% set python_version = "3.12" %}

ReadMe.rst

@@ -78,7 +78,9 @@ Table of Contents
 
    - `Submodule Release Updater`_
 
-9.  `Links`_
+9. `Steps for Updating Rust Tool Chain`_
+
+10.  `Links`_
 
 Continuous Integration (CI)
 ===========================
@@ -379,6 +381,19 @@ the GitHub action.
 
   - `.sync/workflows/leaf/submodule-release-update.yml`
 
+Steps for Updating Rust Tool Chain
+=====================
+
+Steps required to update the Rust tool chain in the Mu DevOps repo. The steps are as follows:
+
+1. Update rust_toolchain in .sync/Version.njk to the new version. PR and merge to main.
+2. Run Build Containers workflow to build a new linux container image (which will use updated .sync/Version.njk).
+3. Update linux_build_container in .sync/Version.njk with the new version. PR and merge to main.
+4. Create new mu_devops tag (GitHub release).
+5. Update mu_devops in .sync/Version.njk to the newly generated tag. PR and merge to main.
+6. Run Sync Mu DevOps Files to Mu Repos workflow to sync the new version to all Mu repos.
+7. Complete associated PRs in the Mu repos.
+
 Links
 =====
 - `Basic Azure Landing Site <https://docs.microsoft.com/en-us/azure/devops/pipelines/?view=azure-devops>`_