Oh, well, I guess it makes sense, since jsq isn't an R package on CRAN or Bioconductor. 
It looks like jsq is a jamovi library, but I'm not sure how exactly that translates into R outside of the jamovi program. It says on the jamovi library page that:
You can download them from here and sideload them into jamovi, but its easier if you access the jamovi library from inside jamovi itself.
It also looks like the R editor inside of jamovi isn't compatible with R versions 3.5 or newer.
Rj - Editor to run R code inside jamovi
Provides an editor allowing you to enter R code, and analyse your data using R inside jamovi. Note that when using the 'System R', Rj is currently not compatible with R 3.5 or newer.
Are you asking more generally about doing Bayesian linear regression in R? If so, there's a tutorial here that uses Stan (rstan). Other popular R packages include brms, JAGS, and rstanarm (I'm sure there are more).
You might want to check out the CRAN Task View for Bayesian modeling. That has short descriptions of what various packages do, and would be a good way to find some that address what you need.