Fix installation instructions

Author: mtfishman

README.md

@@ -14,7 +14,7 @@ A module defining a set of basic types which are place holders for allocated bit
 ```julia
 julia> using Pkg: Pkg
 
-julia> Pkg.add("https://github.com/ITensor/UnspecifiedTypes.jl")
+julia> Pkg.add(url="https://github.com/ITensor/UnspecifiedTypes.jl")
 ```
 
 ## Examples

examples/README.jl

@@ -15,7 +15,7 @@
 ```julia
 julia> using Pkg: Pkg
 
-julia> Pkg.add("https://github.com/ITensor/UnspecifiedTypes.jl")
+julia> Pkg.add(url="https://github.com/ITensor/UnspecifiedTypes.jl")
 ```
 =#