Add link to blog post from runfiles/README.md (#331)

The blog post "Migrating to Bazel Modules (a.k.a. Bzlmod) - Repo Names
and Runfiles" is now live:

- https://blog.engflow.com/2024/08/09/migrating-to-bazel-modules-aka-bzlmod---repo-names-and-runfiles/

Author: mbland

runfiles/README.md

@@ -1,7 +1,7 @@
 # EngFlow Runfiles Libraries Demo
 
-This is an example repository for an upcoming EngFlow blog post, "Migrating
-to Bazel Modules (a.k.a. Bzlmod) - Repo Names and Runfiles".
+This is the example code for the EngFlow blog post "[Migrating to Bazel
+Modules (a.k.a. Bzlmod) - Repo Names and Runfiles][blog]."
 
 - `engflow` contains the main repository of the example
 - `frobozz` is a separate Bazel module representing an external dependency
@@ -14,3 +14,5 @@ bazel run //:runfiles_demo
 bazel build //:runfiles_genrule_demo &&
     cat bazel-bin/demo_output.txt
 ```
+
+[blog]: https://blog.engflow.com/2024/08/09/migrating-to-bazel-modules-aka-bzlmod---repo-names-and-runfiles/