doc: fence command examples in release guide

Put the command examples for finding and replacing the `REPLACEME`
tags into code fences so that they are more easily copiable when
viewing the guide in the GitHub web UI.

PR-URL: #39544
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Beth Griggs <bgriggs@redhat.com>
Reviewed-By: Danielle Adams <adamzdanielle@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/guides/releases.md

@@ -345,10 +345,14 @@ accordingly by removing the bold styling from the previous release.
 If this release includes new APIs then it is necessary to document that they
 were first added in this version. The relevant commits should already include
 `REPLACEME` tags as per the example in the
-[docs README](../../tools/doc/README.md). Check for these tags with `grep
-REPLACEME doc/api/*.md`, and substitute this node version with `sed -i
-"s/REPLACEME/$VERSION/g" doc/api/*.md` or `perl -pi -e "s/REPLACEME/$VERSION/g"
-doc/api/*.md`.
+[docs README](../../tools/doc/README.md). Check for these tags with
+```console
+grep REPLACEME doc/api/*.md
+```
+and substitute this node version with
+```console
+sed -i "s/REPLACEME/$VERSION/g" doc/api/*.md` or `perl -pi -e "s/REPLACEME/$VERSION/g" doc/api/*.md
+```
 
 `$VERSION` should be prefixed with a `v`.