docs(grid) fix missing article
The Grid layout is a subset of [CSS Flexbox](https://css-tricks.com/snippets/css/complete-guide-grid/).
-It can arrange items into 2D "table" that has rows or columns (tracks). The item can span through multiple columns or rows.
+It can arrange items into a 2D "table" that has rows or columns (tracks). The item can span through multiple columns or rows.
The track's size can be set in pixel, to the largest item (`LV_GRID_CONTENT`) or in "Free unit" (FR) to distribute the free space proportionally.
To make an object a grid container call `lv_obj_set_layout(obj, LV_LAYOUT_GRID)`.
