Documentation of initial conditions that depend on a parameter

[TorkelE]

It is possible for an initial condition to be a parameter:

using Catlyst
rn = @reaction_network begin
  @species X(t)=1.0
  @parameters p=1.0 d=0.1
  p, 0 --> X
  d, X --> ∅
end

using DifferentialEquations, Plots
u0 = []
tspan = (0.0, 10.0)
p = []
oprob = ODEProblem(rn, u0, tspan, p)
sol = solve(oprob)
plot(sol)

which is actually quite neat. We don't document (or test) this feature though, so I have added both.

[isaacsas]

Aside from that one comment LGTM. Thanks!