steamos-readonly: add examples (#21480)

pages/linux/steamos-readonly.md

@@ -3,6 +3,10 @@
 > Set the readonly status of the filesystem.
 > More information: <https://gitlab.com/users/evlaV/projects>.
 
+- View the filesystem mutability status:
+
+`steamos-readonly status`
+
 - Set the filesystem to be mutable:
 
 `sudo steamos-readonly disable`
@@ -10,3 +14,7 @@
 - Set the filesystem to be read only:
 
 `sudo steamos-readonly enable`
+
+- Toggle the filesystem mutability:
+
+`sudo steamos-readonly toggle`