add example data to sciene base

Reviewer comment:

-The README.md mentions that the metaipm-example repository requires outputs from the carp-demographic-rates repository. The csv files with posterior distributions in wide format needed (e.g., “vb_posterior_silver_wide.csv”) are not present in every branch of the carp-demographic-rates repository, as far as I can tell. I grabbed the existing csv files from the “UMR2021” branch, rather than trying to re-run the analysis in the v1.0 branch. I wonder if you could just put copies of the required csv files in the metaipm-example repository as well? It is redundant in some ways, but it would save users from having to recreate the files necessary for metaipm-example.

A solution to this issue is to host the input data on another site such as ScienceBase.