docs(readme): say how to get a sidecar before explaining how it is used

The shard integration section documented the contract in detail but never
told an admin where the base URL, WS URL, protocol version and token come
from. They come from the installer, which prints them at the end of a run.

Co-Authored-By: Claude <noreply@anthropic.com>

README.md

@@ -416,6 +416,29 @@ exposes a small, authenticated HTTP + WebSocket API; this website is a *client*
 itself is never exposed to the internet — only the sidecar is, and only the website's backend talks
 to it.
 
+### Setting up the shard side
+
+You do not build or place any of it by hand. The
+**[Runic Gateway installer](https://gitea.whitlocktech.com/RunicGateway/installer)** runs on the
+shard host, deploys the ServUO plugin and the uo-link sidecar as a matched, protocol-checked pair,
+registers the sidecar as a service, and ends by printing the four values this site needs:
+
+```
+Base URL          http://<shard-host>:8080
+WebSocket URL     ws://<shard-host>:8080/ws
+Protocol version  3
+Auth token        4f9c…
+```
+
+Paste them into **Admin → Shard** here and the bridge is live. The operator guide is
+[installer/INSTALL.md](https://gitea.whitlocktech.com/RunicGateway/docs/src/branch/main/installer/INSTALL.md);
+its [Appendix A](https://gitea.whitlocktech.com/RunicGateway/docs/src/branch/main/installer/INSTALL.md#appendix-a--installing-by-hand)
+is the same deployment done by hand, still supported, for a host that cannot run the binary or a
+developer working from a source tree.
+
+Nothing here needs the shard to exist: with no sidecar configured the site renders normally and
+shows the shard offline.
+
 ### How it works
 
 ```