Document flexing

Reviewed By: danielbuechele

Differential Revision: D6976135

fbshipit-source-id: e9051b1e583d909aefe76f7aa9505467890a0d4c

website/contents/properties/flex.md

@@ -6,3 +6,32 @@ editableProperties: ['flexGrow', 'flexShrink', 'flexBasis']
 ---
 
 ## Flex Basis, Grow, and Shrink
+
+### Flex Grow
+
+Flex grow describes how any space within a container should be distributed
+among its children along the main axis. After laying out its children, a container will
+distribute any remaining space according to the flex grow values specified by its children.
+
+flex grow accepts any floating point value >= 0, with 0 being the default value.
+A container will distribute any remaining space among its children weighted by the child’s flex grow value.
+
+### Flex Shrink
+
+Flex shrink describes how to shrink children along the main axis in the
+case that the total size of the children overflow the size of the container on the main axis.
+flex shrink is very similar to flex grow and can be thought of in the same way if
+any overflowing size is considered to be negative remaining space.
+These two properties also work well together by allowing children to grow and shrink as needed.
+
+flex shrink accepts any floating point value >= 0, with 1 being the default value.
+A container will shrink its children weighted by the child’s flex shrink value.
+
+### Flex Basis
+
+Flex basis is an axis-independent way of providing the default size of an item
+along the main axis. Setting the flex basis of a child is similar to setting the Width of that
+child if its parent is a container with FlexDirection = row or setting the Height of a child
+if its parent is a container with FlexDirection = column. The flex basis of an item is the 
+efault size of that item, the size of the item before any flex grow and flex shrink
+calculations are performed.