docs(level): expands design guidelines for level layout. (#3673)

* docs: expands design guidelines for level layout.

* Expands content.

* Image placeholders.

* Adds content to ready for review.

* Apply suggestions from code review

* Remove image placeholders

packages/documentation-site/patternfly-docs/content/design-guidelines/layouts/level.md

@@ -2,4 +2,21 @@
 id: Level
 section: layouts
 ---
-Use a **Level** layout to evenly distribute content horizontally within a container.
+The **level** layout is designed to distribute space evenly between sections of content and center them horizontally. 
+
+## Elements
+
+By default, level items are placed on the page horizontally and wrap. The level layout is not responsive, but items will wrap as the viewport is resized.
+
+A level layout will contain:
+
+1. **Level:** The level container, which holds all level items.
+1. **Level item:** An individual section of content to be placed in the level container. 
+
+## Usage
+
+The level layout can be used to ensure that sections of content are neatly and evenly displayed across the width of a UI.
+
+## Variations
+
+To adjust spacing between items, you can apply gutters.