docs/oasis-node/cli: Document prune command

Author: martintomazic

docs/oasis-node/cli.md

@@ -364,3 +364,26 @@ may stay constant or not be reclaimed for a very long time.
 
 This command gives operators manual control to release disk space during
 maintenance periods.
+
+### prune-experimental
+
+Run
+
+```sh
+oasis-node storage prune-experimental --config /path/to/config/file
+```
+
+to trigger manual pruning of consensus database instances:
+
+```sh
+{"caller":"storage.go:433","level":"info","module":"cmd/storage", \
+"msg":"Starting consensus databases pruning. This may take a while...", \
+"ts":"2025-10-23T11:02:11.129822974Z"}
+```
+
+Operatos should run this whenever they change pruning configuration, e.g. when
+enabling it for the first time, or later changing it to retain less data. This
+way they guarantee the node is healthy when it starts.
+
+Following successful pruning, to release disk space, they are encouraged to run
+[the compaction command](#compact-experimental).