add setup instructions to each tutorial

[isaacsas]

We should consider adding a new starting section to each tutorial that shows how to install the needed packages in a clean environment. This would make them more self-contained for users.

[TorkelE]

You mean having a

using Pkg
Pkg.activate(".")
Pkg.add("Catalyst")
Pkg.add("BifurcationKit")
Pkg.add("Plots")

a the beginning.

Some tutorials are already rather long (mostly my fault), so a bit reluctant to expand them further with something that is fairly straightforward. Although I could see it being convenient in some cases. Maybe make it standard to put it at the end (although that ruins the convenience factor and is only useful when people realise that is standard). If we could make a collapsed by expandable section at the top of the tutorial with a title "Tutorial environment set-up" or similar, that would probably be ideal.

[isaacsas]

People can just skip the section, but this way they can cut and paste code to run the full tutorial.