Update README.

Author: samuelsonric

README.md

@@ -5,7 +5,7 @@ sparse semidefinite constraints.
 
 ## Basic Usage
 
-The `sdplib` directory contains three semidefinite programming problems from the [SDPLIB library](https://github.com/vsdp/SDPLIB). The function `construct_model`, defined below, reads one of the problems and constructs a [JuMP.jl](https://github.com/jump-dev/JuMP.jl) model.
+The `sdplib` directory contains four semidefinite programming problems from the [SDPLIB library](https://github.com/vsdp/SDPLIB). The function `construct_model`, defined below, reads one of the problems and constructs a [JuMP.jl](https://github.com/jump-dev/JuMP.jl) model.
 
 ```julia-repl
 julia> using FileIO, LinearAlgebra, JuMP