Updated docs

docs/README.md

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+# PVE Exporter Documentation
+
+PVE Exporter periodically collects monitoring data from the Proxmox VE HTTP API
+and stores the latest values in the Prometheus registry exposed at `/metrics`.
+
+## Guides
+
+- [Configuration reference](configuration.md) describes every YAML setting,
+  API token permissions, and collector switch.
+- [Metrics reference](metrics.md) lists exported metrics, labels, units, and
+  numeric state mappings.
+- [Operations and troubleshooting](operations.md) covers native and container
+  deployment, endpoint failover, logging, security, and common errors.
+- [Architecture and adding collectors](architecture.md) explains the collection
+  flow and how the main packages fit together.
+
+## Important behavior
+
+- One exporter instance is intended for one standalone node or one PVE cluster.
+- Multiple configured API hosts provide redundant access to that same cluster.
+- Collection runs every `proxmox.interval` seconds independently of Prometheus
+  scrapes.
+- Collector label sets that stop receiving updates are removed after five
+  minutes.
+- The only application HTTP endpoint is `/metrics`.