Update README with link to josh-sync

Author: Kobzol

library/stdarch/README.md

@@ -19,49 +19,6 @@ The `std::simd` component now lives in the
 
 ## Synchronizing josh subtree with rustc
 
-This repository is linked to `rust-lang/rust` as a [josh](https://josh-project.github.io/josh/intro.html) subtree. You can use the following commands to synchronize the subtree in both directions.
+This repository is linked to `rust-lang/rust` as a [josh](https://josh-project.github.io/josh/intro.html) subtree. You can use the [rustc-josh-sync](https://github.com/rust-lang/josh-sync) tool to perform synchronization.
 
-You'll need to install `josh-proxy` locally via
-
-```
-cargo install josh-proxy --git https://github.com/josh-project/josh --tag r24.10.04
-```
-Older versions of `josh-proxy` may not round trip commits losslessly so it is important to install this exact version.
-
-### Pull changes from `rust-lang/rust` into this repository
-
-1) Checkout a new branch that will be used to create a PR into `rust-lang/stdarch`
-2) Run the pull command
-    ```
-    cargo run --manifest-path josh-sync/Cargo.toml rustc-pull
-    ```
-3) Push the branch to your fork and create a PR into `stdarch`
-
-### Push changes from this repository into `rust-lang/rust`
-
-NOTE: If you use Git protocol to push to your fork of `rust-lang/rust`,
-ensure that you have this entry in your Git config,
-else the 2 steps that follow would prompt for a username and password:
-
-```
-[url "git@github.com:"]
-insteadOf = "https://github.com/"
-```
-
-1) Run the push command to create a branch named `<branch-name>` in a `rustc` fork under the `<gh-username>` account
-    ```
-    cargo run --manifest-path josh-sync/Cargo.toml rustc-push <branch-name> <gh-username>
-    ```
-2) Create a PR from `<branch-name>` into `rust-lang/rust`
-
-#### Minimal git config
-
-For simplicity (ease of implementation purposes), the josh-sync script simply calls out to system git. This means that the git invocation may be influenced by global (or local) git configuration.
-
-You may observe "Nothing to pull" even if you *know* rustc-pull has something to pull if your global git config sets `fetch.prunetags = true` (and possibly other configurations may cause unexpected outcomes).
-
-To minimize the likelihood of this happening, you may wish to keep a separate *minimal* git config that *only* has `[user]` entries from global git config, then repoint system git to use the minimal git config instead. E.g.
-
-```
-GIT_CONFIG_GLOBAL=/path/to/minimal/gitconfig GIT_CONFIG_SYSTEM='' cargo run --manifest-path josh-sync/Cargo.toml -- rustc-pull
-```
+You can find a guide on how to perform the synchronization [here](https://rustc-dev-guide.rust-lang.org/external-repos.html#synchronizing-a-josh-subtree).