CI: Add Aqua badge (#134)

Author: inkydragon

README.md

@@ -4,6 +4,7 @@ A general framework for fast Fourier transforms (FFTs) in Julia.
 
 [![GHA](https://github.com/JuliaMath/AbstractFFTs.jl/workflows/CI/badge.svg)](https://github.com/JuliaMath/AbstractFFTs.jl/actions?query=workflow%3ACI+branch%3Amaster)
 [![Codecov](http://codecov.io/github/JuliaMath/AbstractFFTs.jl/coverage.svg?branch=master)](http://codecov.io/github/JuliaMath/AbstractFFTs.jl?branch=master)
+[![Aqua QA](https://raw.githubusercontent.com/JuliaTesting/Aqua.jl/master/badge.svg)](https://github.com/JuliaTesting/Aqua.jl)
 
 Documentation:
 [![](https://img.shields.io/badge/docs-stable-blue.svg)](https://JuliaMath.github.io/AbstractFFTs.jl/stable)