docs: add step 0 -- clone the repo onto the server

First-run was missing the git clone command entirely.
Uses the `authelia` branch name since that's the long-term home
for this stack (separate from the `main` Frigate branch).

https://claude.ai/code/session_012eTokAaGiZo7aGt1T2W9BC

README.md

@@ -116,6 +116,12 @@ Look for any of these in the app's docs:
 ## First-run setup
 
 ```bash
+# 0) Clone the repo onto the server (auth stack -- separate from the
+#    Frigate stack which lives on the `main` branch).
+git clone -b authelia https://github.com/outis1one/frigate_w_audio.git \
+    ~/docker/authelia
+cd ~/docker/authelia
+
 # 1) Create the external docker network (Caddy must also be on this).
 docker network create caddy_net 2>/dev/null || true