Flexbox docs

Updated the flexbox documentation for the current flexbox implementation

docs/objects/Flexbox/setFlexShrink.md

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+## setFlexShrink
+
+### Description
+
+The `setFlexShrink` method sets the shrink factor of a child object within the Flexbox container. This value determines how much the child should shrink relative to the rest of the objects in the flex container, if necessary.
+
+### Parameters
+
+1. `number` The shrink factor of the child object. The default is 0. A higher value will cause the object to shrink more.
+
+### Returns
+
+1. `object` The object in use
+
+### Usage
+
+* Creates a default Flexbox, adds some objects to it, and sets the flexShrink for the first object.
+
+```lua
+local main = basalt.createFrame()
+local flexbox = mainFrame:addFlexbox()
+local object1 = flexbox:addButton()
+object1:setFlexShrink(2) -- this object will shrink twice as much as the others if necessary
+```