more docs for flowpipe plotting opts

[mforets]

• ORBIT with / without markers

for example, to join the point of ORBIT:

A = state_matrix(ivp)
X0 = initial_state(ivp)
prob = @ivp(x' = A*x, x(0) ∈ X0)
sol = solve(prob, alg=ORBIT(δ=0.1), NSTEPS=10);

# with marker and path
plot(sol, vars=(0, 1), seriestype=:path)

# without marker and path
plot(sol, vars=(0, 1), seriestype=:path, marker=:none)

# with different marker and path
plot(sol, vars=(0, 1), seriestype=:path, marker=:utriangle)

cc @dfcaporale