Missing code lines in the documentation

[Armavica]

Hi, as part of the review that I am doing for JOSS (openjournals/joss-reviews#9384) I am going through the diffsol book.

Thank you for fixing issue #216. I managed to run this example using the file in the repository, but because the file changed, the documentation is now missing some lines. If you copy-paste all of the codeblocks from this page you get a non-compiling file.

[martinjrobins]

:( yea I keep running into this with the examples that use line numbers to include the examples. If you know of a better way to keep these in sync please let me know. For now I've just adjusted them manually in #234

[martinjrobins]

looks like this is fixed now (https://martinjrobins.github.io/diffsol/primer/population_dynamics_fitting.html)