docs: fix system-prune markdown; reword for clarity
In addition to tweaking markdown, reword the explanation of
the "--volumes" option for clarity.
@@ -9,9 +9,9 @@ podman\-system\-prune - Remove all unused container, image and volume data
## DESCRIPTION
**podman system prune** removes all unused containers (both dangling and unreferenced), pods and optionally, volumes from local storage.
-With the `all` option, you can delete all unused images. Unused images are dangling images as well as any image that does not have any containers based on it.
+With the **--all** option, you can delete all unused images. Unused images are dangling images as well as any image that does not have any containers based on it.
-By default, volumes are not removed to prevent important data from being deleted if there is currently no container using the volume. Use the --volumes flag when running the command to prune volumes as well.
+By default, volumes are not removed to prevent important data from being deleted if there is currently no container using the volume. Use the **--volumes** flag when running the command to prune volumes as well.
## OPTIONS
**--all**, **-a**
@@ -28,7 +28,7 @@ Print usage statement
**--volumes**
-Prune volumes not used by at least one container
+Prune volumes currently unused by any container
## SEE ALSO
podman(1), podman-image-prune(1), podman-container-prune(1), podman-pod-prune(1), podman-volume-prune(1)
