viewnior: add page (#2012)

pages/linux/viewnior.md

@@ -0,0 +1,15 @@
+# viewnior
+
+> Simple and elegant image viewer.
+
+- View an image:
+
+`viewnior {{path/to/image.ext}}`
+
+- View in fullscreen mode:
+
+`viewnior --fullscreen {{path/to/image.ext}}`
+
+- View fullscreen in slideshow mode:
+
+`viewnior --slideshow {{path/to/image.ext}}`