[Explanation](https://bevyengine.org/learn/contribute/helping-out/explaining-examples/)
for the 2d shapes example, taken from the original HackMD document and
edited a bit.
This example is a strange one, it's eye-catching mostly because it's the
first example (at time of writing) in the examples page. That being
said, the example does a decent amount of teaching utility to it: we can
explain the bevy math-shape to mesh pipeline, which illuminates a way of
transforming one form of data (abstract, mathematical shape
descriptions) into another (meshes) which may be novel or inspirational
to some users.
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Co-authored-by: theotherphil <phil.j.ellison@gmail.com>
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