update README, add geyser sample (as per quickstart in README)

geyser_on_off.py

@@ -0,0 +1,23 @@
+import os
+import panel
+from typing import Any
+
+from watt42_viewlib import attach_w42_state
+
+SYSTEM_ID = os.environ.get("WATT42_SYSTEM_ID", "invalid-system-id")
+API_TOKEN = os.environ.get("WATT42_API_TOKEN", "invalid-api-token")
+
+w42_state = panel.rx(None)
+
+attach_w42_state(rx_var=w42_state, system_id=SYSTEM_ID, token=API_TOKEN)
+
+def get_geyser_state(state: dict[str, Any]) -> bool:
+    if not state:
+        return False
+    return state.get("is_geyser_on", False)
+
+geyser_state = panel.rx(get_geyser_state)(w42_state)
+
+indicator = panel.indicators.BooleanStatus(value=geyser_state, name="W42 Connected", color="success")
+
+_ = indicator.servable()