Docs for the `ArnoldiWorkspace(n, k)` constructor

[yakovbraver]

The docs provide the following example:

# allocates workspace for 20-dimensional Krylov subspace
arnoldi = ArnoldiWorkspace(100, 20)

This gives a MethodError because the relevant constructor is ArnoldiWorkspace(::Type{T}, ::Int64, ::Int64) where T. Should be e.g.

arnoldi = ArnoldiWorkspace(ComplexF32, 100, 20)

(Maybe add a default value for the type argument?)