The recommendation is to install from CRAN.
install.packages("bmp")
You can, however, use the remotes package to install the development version:
if (!require("remotes")) install.packages("remotes")
# remotes::install_github("jefferis/bmp")
install.packages("bmp", repos = c('https://jefferis.r-universe.dev', 'https://cloud.r-project.org'))
NB Windows users need Rtools and devtools to install this way.