Flexbox docs

Updated the flexbox documentation for the current flexbox implementation

docs/objects/Flexbox/setFlexGrow.md

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+## setFlexGrow
+
+### Description
+
+The `setFlexGrow` method sets the grow factor of a child object within the Flexbox container. This determines how much of the remaining space along the main axis the child should take up, in relation to the other children. A larger grow factor means the child will take up more of the remaining space.
+
+### Parameters
+
+1. `number` The grow factor for the child object. This should be a non-negative number. A value of 0 means the child will not grow beyond its initial size. Default is 0.
+
+### Returns
+
+1. `object` The object in use
+
+### Usage
+
+* Creates a default Flexbox, adds some objects to it, and sets the flexGrow for the first object.
+
+```lua
+local main = basalt.createFrame()
+local flexbox = mainFrame:addFlexbox()
+local object1 = flexbox:addButton()
+object1:setFlexGrow(1) -- this object will grow to take up remaining space
+local object2 = flexbox:addButton() -- this object will not grow
+```