Friendlier homepage with usage instructions (#86)

* Friendlier homepage with usage instructions

* newlines

README.md

@@ -1,9 +1,36 @@
 # FFTW.jl
 
+[![Travis](https://travis-ci.org/JuliaMath/FFTW.jl.svg?branch=master)](https://travis-ci.org/JuliaMath/FFTW.jl)
+[![AppVeyor](https://ci.appveyor.com/api/projects/status/hofbdbyt287qn49s/branch/master?svg=true)](https://ci.appveyor.com/project/ararslan/fftw-jl/branch/master)
+[![Coveralls](https://coveralls.io/repos/github/JuliaMath/FFTW.jl/badge.svg?branch=master)](https://coveralls.io/github/JuliaMath/FFTW.jl?branch=master)
+
+[![](https://img.shields.io/badge/docs-stable-blue.svg)](https://JuliaMath.github.io/FFTW.jl/stable)
+[![](https://img.shields.io/badge/docs-latest-blue.svg)](https://JuliaMath.github.io/FFTW.jl/latest)
+
 This package provides Julia bindings to the [FFTW](http:https://www.fftw.org/) library for
 fast Fourier transforms (FFTs), as well as functionality useful for signal processing.
 These functions were formerly a part of Base Julia.
 
+## Usage and documentation
+
+```julia
+]add FFTW
+using FFTW
+fft([0; 1; 2; 1])
+```
+returns
+```
+4-element Array{Complex{Float64},1}:
+ 4.0 + 0.0im
+ -2.0 + 0.0im
+ 0.0 + 0.0im
+ -2.0 + 0.0im
+```
+
+The documentation of generic FFT functionality can be found in the [AbstractFFTs.jl package](https://juliamath.github.io/AbstractFFTs.jl/latest/api.html#Public-Interface-1). Additional functionalities supported by the FFTW library are documented in the present package.
+
+## MKL
+
 Alternatively, the FFTs in Intel's Math Kernel Library (MKL) can be used
 by setting an environment variable `JULIA_FFTW_PROVIDER` to `MKL` and running
 `Pkg.build("FFTW")`. If Julia was built with MKL, then Julia's MKL will be
@@ -15,6 +42,9 @@ Note however that MKL provides only a subset of the functionality provided by FF
 Intel's [documentation](https://software.intel.com/en-us/mkl-developer-reference-c-using-fftw3-wrappers)
 for more information about potential differences or gaps in functionality.
 
+
+## License
+
 The FFTW library will be downloaded on versions of Julia where it is no longer distributed
 as part of Julia.
 Note that FFTW is licensed under GPLv2 or higher (see
@@ -29,11 +59,3 @@ If you distribute a derived or combined work, i.e. a program that links to and i
 with the FFTW library, then that distribution falls under the terms of the GPL.
 If you just distribute source code that links to FFTW.jl, and users have to download FFTW
 or MKL to provide the backend, then the GPL probably doesn't have much effect on you.
-
-[![Travis](https://travis-ci.org/JuliaMath/FFTW.jl.svg?branch=master)](https://travis-ci.org/JuliaMath/FFTW.jl)
-[![AppVeyor](https://ci.appveyor.com/api/projects/status/hofbdbyt287qn49s/branch/master?svg=true)](https://ci.appveyor.com/project/ararslan/fftw-jl/branch/master)
-[![Coveralls](https://coveralls.io/repos/github/JuliaMath/FFTW.jl/badge.svg?branch=master)](https://coveralls.io/github/JuliaMath/FFTW.jl?branch=master)
-
-Documentation:
-[![](https://img.shields.io/badge/docs-stable-blue.svg)](https://JuliaMath.github.io/FFTW.jl/stable)
-[![](https://img.shields.io/badge/docs-latest-blue.svg)](https://JuliaMath.github.io/FFTW.jl/latest)