That is probably because figures is not included in the site_build process. I'm not sure what the convention is, but it might be better to move figures to man/figures, as is done here for example: https://github.com/r-lib/pkgdown/tree/master/man/figures
The figure at https://github.com/inbo/wateRinfo/blob/master/figures/README-plot_pressure-1.png which is referenced in the README is not rendered on the website:
https://inbo.github.io/wateRinfo/
That is probably because figures is not included in the site_build process. I'm not sure what the convention is, but it might be better to move
figures
toman/figures
, as is done here for example: https://github.com/r-lib/pkgdown/tree/master/man/figures