Add installation instructions

Author: logankilpatrick

docs/src/index.md

@@ -10,6 +10,21 @@ end
 
 *StatsBase.jl* is a Julia package that provides basic support for statistics. Particularly, it implements a variety of statistics-related functions, such as scalar statistics, high-order moment computation, counting, ranking, covariances, sampling, and empirical density estimation.
 
+## Getting Started
+
+To install StatsBase through the Julia REPL, you can type `] add StatsBase` or:
+
+```julia
+using Pkg
+Pkg.add("StatsBase")
+```
+To load the package, use the command:
+
+```
+using StatsBase
+```
+
+## Available methods
 
 ```@contents
 Pages = ["weights.md", "scalarstats.md", "robust.md", "deviation.md", "cov.md", "counts.md", "ranking.md", "sampling.md", "empirical.md", "signalcorr.md", "misc.md", "statmodels.md", "transformations.md"]