Instructions for git_override in release notes

.github/workflows/release_notes_template.txt

@@ -5,6 +5,15 @@ If you're using `bzlmod`, add the following to `MODULE.bazel`:
 ```starlark
 bazel_dep(name = "toolchains_llvm", version = "{tag}")
 
+# To directly use a commit from GitHub, replace commit with the commit you want.
+# Otherwise, omit this block.
+git_override(
+  module_name = "toolchains_llvm",
+  commit = "{commit}",
+  remote = "https://github.com/grailbio/bazel-toolchain",
+)
+
+# Configure and register the toolchain.
 llvm = use_extension("@toolchains_llvm//toolchain/extensions:llvm.bzl", "llvm")
 llvm.toolchain(
    llvm_version = "16.0.0",

.github/workflows/release_prep.sh

@@ -7,7 +7,8 @@ git config user.name "Your Name"
 
 # Set by GH actions, see
 # https://docs.github.com/en/actions/learn-github-actions/environment-variables#default-environment-variables
-tag=${GITHUB_REF_NAME}
+tag="${GITHUB_REF_NAME}"
+commit="${GITHUB_SHA}"
 # The prefix is chosen to match what GitHub generates for source archives
 prefix="toolchains_llvm-${tag}"
 archive="toolchains_llvm-${tag}.tar.gz"
@@ -17,6 +18,7 @@ sha=$(shasum -a 256 "${archive}" | cut -f1 -d' ')
 
 sed \
   -e "s/{tag}/${tag}/g" \
+  -e "s/{commit}/${commit}/g" \
   -e "s/{prefix}/${prefix}/g" \
   -e "s/{archive}/${archive}/g" \
   -e "s/{sha}/${sha}/g" \