nitrogen: add page (#7492)

pages/linux/nitrogen.md

@@ -0,0 +1,16 @@
+# nitrogen
+
+> Desktop background browser and setter for X Window.
+> More information: <https://github.com/l3ib/nitrogen>.
+
+- View and set the wallpapers from a specific directory:
+
+`nitrogen {{path/to/directory}}`
+
+- Set the wallpaper with automatic size settings:
+
+`nitrogen --set-auto {{path/to/file}}`
+
+- Restore the previous wallpaper:
+
+`nitrogen --restore`