update README

Author: mohamed82008

README.md

@@ -1 +1,65 @@
-# DistributionsAD.jl
+# DistributionsAD.jl
+
+This package defines the necessary functions to enable automatic differentiation (AD) of the `logpdf` function from [Distributions.jl](https://github.com/JuliaStats/Distributions.jl) using the packages [Tracker.jl](https://github.com/FluxML/Tracker.jl) and [ForwardDiff.jl](https://github.com/JuliaDiff/ForwardDiff.jl). The goal of this package is to make the output of `logpdf` differentiable wrt all continuous parameters of a distribution as well as the random variable in the case of continuous distributions.
+
+AD of `logpdf` is fully supported and tested for the following distributions wrt all combinations of continuous variables (distribution parameters and/or the random variable) and using all defined distribution constructors:
+- Univariate discrete
+    - `Bernoulli`
+    - `BetaBinomial`
+    - `Binomial`
+    - `Categorical`
+    - `Geometric`
+    - `NegativeBinomial`
+    - `Poisson`
+    - `PoissonBinomial`
+    - `Skellam`
+- Univariate continuous
+    - `Arcsine`
+    - `Beta`
+    - `BetaPrime`
+    - `Biweight`
+    - `Cauchy`
+    - `Chernoff`
+    - `Chi`
+    - `Chisq`
+    - `Cosine`
+    - `Epanechnikov`
+    - `Erlang`
+    - `Exponential`
+    - `FDist`
+    - `Frechet`
+    - `Gamma`
+    - `GeneralizedExtremeValue`
+    - `GeneralizedPareto`
+    - `Gumbel`
+    - `InverseGamma`
+    - `InverseGaussian`
+    - `Kolmogorov`
+    - `Laplace`
+    - `Levy`
+    - `LocationScale`
+    - `Logistic`
+    - `LogitNormal`
+    - `LogNormal`
+    - `Normal`
+    - `NormalCanon`
+    - `NormalInverseGaussian`
+    - `Pareto`
+    - `PGeneralizedGaussian`
+    - `Rayleigh`
+    - `Semicircle`
+    - `SymTriangularDist`
+    - `TDist`
+    - `TriangularDist`
+    - `Triweight`
+    - `Uniform`
+    - `Weibull`
+- Multivariate continuous
+    - `MvLogNormal`
+    - `MvNormal`
+- Matrix-variate continuous
+    - `MatrixBeta`
+
+# Get Involved
+
+A number of distributions are still either broken or not fully supported for various reasons. See [this issue](https://github.com/TuringLang/DistributionsAD.jl/issues/2). If you can fix any of the broken ones, a PR is welcome!