[docs] big bang update (#348)

* [docs] big bang update

* Simplified polluted README.md by moving parts to the documentation
* Removed duplicates with `pymdownx.snippets` extension
* Enabled code copy
* Extended "Getting Started"
* Added "Monitoring" page
* Separated "Upgrade" page
* Added default config yaml to docs

Signed-off-by: Dmytro Bondar <git@bonddim.dev>

* Update sources.md

Co-authored-by: h44z <christoph.h@sprinternet.at>

---------

Signed-off-by: Dmytro Bondar <git@bonddim.dev>
Co-authored-by: h44z <christoph.h@sprinternet.at>

docs/documentation/monitoring/prometheus.md

@@ -0,0 +1,32 @@
+By default WG-Portal exposes Prometheus metrics on port `8787` if interface/peer statistic data collection is enabled.
+
+## Exposed Metrics
+
+| Metric                                     | Type  | Description                                    |
+|--------------------------------------------|-------|------------------------------------------------|
+| `wireguard_interface_received_bytes_total` | gauge | Bytes received through the interface.          |
+| `wireguard_interface_sent_bytes_total`     | gauge | Bytes sent through the interface.              |
+| `wireguard_peer_last_handshake_seconds`    | gauge | Seconds from the last handshake with the peer. |
+| `wireguard_peer_received_bytes_total`      | gauge | Bytes received from the peer.                  |
+| `wireguard_peer_sent_bytes_total`          | gauge | Bytes sent to the peer.                        |
+| `wireguard_peer_up`                        | gauge | Peer connection state (boolean: 1/0).          |
+
+## Prometheus Config
+
+Add following scrape job to your Prometheus config file:
+
+```yaml
+# prometheus.yaml
+scrape_configs:
+  - job_name: wg-portal
+    scrape_interval: 60s
+    static_configs:
+      - targets:
+          - localhost:8787 # Change localhost to IP Address or hostname with WG-Portal
+```
+
+# Grafana Dashboard
+
+You may import [`dashboard.json`](https://github.com/h44z/wg-portal/blob/master/deploy/helm/files/dashboard.json) into your Grafana instance.
+
+![Dashboard](../../assets/images/dashboard.png)