Mention that compiler-builtins is now using `rustc-josh-sync`
diff --git a/src/doc/rustc-dev-guide/src/external-repos.md b/src/doc/rustc-dev-guide/src/external-repos.md
index 0f73223..68986a0 100644
--- a/src/doc/rustc-dev-guide/src/external-repos.md
+++ b/src/doc/rustc-dev-guide/src/external-repos.md
@@ -44,7 +44,7 @@
* `miri` ([sync guide](https://github.com/rust-lang/miri/blob/master/CONTRIBUTING.md#advanced-topic-syncing-with-the-rustc-repo))
* `rust-analyzer` ([sync script](https://github.com/rust-lang/rust-analyzer/blob/2e13684be123eca7181aa48e043e185d8044a84a/xtask/src/release.rs#L147))
* `rustc-dev-guide` ([josh sync](#synchronizing-a-josh-subtree))
- * `compiler-builtins`
+ * `compiler-builtins` ([josh sync](#synchronizing-a-josh-subtree))
* `stdarch` ([josh sync](#synchronizing-a-josh-subtree))
### Josh subtrees
@@ -56,6 +56,7 @@
We use a dedicated tool called [`rustc-josh-sync`][josh-sync] for performing Josh subtree updates.
Currently, we are migrating Josh repositories to it. So far, it is used in:
+- compiler-builtins
- rustc-dev-guide
- stdarch
