Update README.md

Author: ChrisRackauckas

README.md

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 [![codecov.io](http://codecov.io/github/ChrisRackauckas/DiffEqDiffTools.jl/coverage.svg?branch=master)](http://codecov.io/github/ChrisRackauckas/DiffEqDiffTools.jl?branch=master)
 
 DiffEqDiffTools.jl is a component package in the DifferentialEquations ecosystem. It holds the common tools for taking derivatives, Jacobians, etc. and utilizing the traits from the ParameterizedFunctions when possible for increasing the speed of calculations. Users interested in using this functionality should check out [DifferentialEquations.jl](https://github.com/JuliaDiffEq/DifferentialEquations.jl/blob/master/src/DifferentialEquations.jl).
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+Note: This is currently a work in progress. Anyways, it will be behind the scenes. If you're interesting in helping develop it, please contact Chris Rackauckas.