Add instructions how to persist prometheus docker container data

Signed-off-by: shoce <rslnx@icloud.com>

docs/installation.md

@@ -55,6 +55,23 @@ docker run \
     prom/prometheus
 ```
 
+### Save your Prometheus data
+
+Prometheus data is stored in `/prometheus` dir inside the container, so the data is cleared every time the container gets restarted. To save your data, you need to set up persistent storage (or bind mounts) for your container.
+
+Run Prometheus container with persistent storage:
+
+```bash
+# Create persistent volume for your data
+docker volume create prometheus-data
+# Start Prometheus container
+docker run \
+    -p 9090:9090 \
+    -v /path/to/prometheus.yml:/etc/prometheus/prometheus.yml \
+    -v prometheus-data:/prometheus \
+    prom/prometheus
+```
+
 ### Custom image
 
 To avoid managing a file on the host and bind-mount it, the