Flexbox docs

Updated the flexbox documentation for the current flexbox implementation

docs/objects/Flexbox/getFlexGrow.md

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+## getFlexGrow
+
+### Description
+
+The `getFlexGrow` method retrieves the grow factor of a child object within the Flexbox container. This value determines how much of the remaining space along the main axis the child should take up, in relation to the other children.
+
+### Returns
+
+1. `number` The grow factor of the child object.
+
+### Usage
+
+* Creates a default Flexbox, adds some objects to it, sets the flexGrow for the first object, and then retrieves this value.
+
+```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
+basalt.debug(object1:getFlexGrow()) -- prints 1
+```