Mention that stdarch is managed by josh-sync
diff --git a/src/external-repos.md b/src/external-repos.md
index fc40b5d..0f73223 100644
--- a/src/external-repos.md
+++ b/src/external-repos.md
@@ -43,9 +43,9 @@
* Using the [josh] tool
* `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`
+ * `rustc-dev-guide` ([josh sync](#synchronizing-a-josh-subtree))
* `compiler-builtins`
- * `stdarch`
+ * `stdarch` ([josh sync](#synchronizing-a-josh-subtree))
### Josh subtrees
@@ -57,6 +57,7 @@
Currently, we are migrating Josh repositories to it. So far, it is used in:
- rustc-dev-guide
+- stdarch
To use the tool, first install it with `cargo install --locked --git https://github.com/rust-lang/josh-sync`.
