docs(grid): replace the placeholder descriptions for row/col

src/components/grid/col.ts

@@ -5,7 +5,8 @@ import { Directive } from '@angular/core';
   * @module ionic
   * @description
   *
-  * Column description
+  * Columns are cellular components of the [grid](../Grid) system and go inside of a [row](../Row).
+  * They will expand to fill their row. All content within a grid should go inside of a column.
   *
   * ## Column attributes
   *

src/components/grid/row.ts

@@ -5,7 +5,8 @@ import { Directive } from '@angular/core';
   * @module ionic
   * @description
   *
-  * Row description
+  * Rows are horizontal components of the [grid](../Grid) system and contain varying numbers of
+  * [columns](../Col). They ensure the columns are positioned properly.
   *
   * ## Row attributes
   *