Add a link to instruction to update the VS toolchain.

No-Try: True
Bug: 1006238
Change-Id: I20bc6b5ccb3d2d76bca741b4e4edc43a91f8a692
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1872730Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Mirko Bonadei <mbonadei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708093}

build/vs_toolchain.py

@@ -430,6 +430,8 @@ def _GetDesiredVsToolchainHashes():
   # VS 2019 Update 9 (16.3.29324.140) with 10.0.18362 SDK, 10.0.17763 version of
   # Debuggers, and 10.0.17134 version of d3dcompiler_47.dll, with ARM64
   # libraries.
+  # See go/chromium-msvc-toolchain for instructions about how to update the
+  # toolchain.
   toolchain_hash = '8f58c55897a3282ed617055775a77ec3db771b88'
   # Third parties that do not have access to the canonical toolchain can map
   # canonical toolchain version to their own toolchain versions.