Add a single-parameter gutter example

Author: agriyakhetarpal

layouts/shortcodes/grid.html

@@ -118,6 +118,28 @@
 
 {{< /grid >}}
 
+Here's a grid with gutters. A single value applies to all breakpoints.
+
+{{< grid columns="1 2 3 4" gutter="1" >}}
+
+[[item]]
+type = 'card'
+body = 'Tight spacing'
+
+[[item]]
+type = 'card'
+body = 'Tight spacing'
+
+[[item]]
+type = 'card'
+body = 'Tight spacing'
+
+[[item]]
+type = 'card'
+body = 'Tight spacing'
+
+{{< /grid >}}
+
 */}}
 
 {{- $items := "" -}}