Improve doc for bookdown with CI

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Update vignette part on Bookdown with:

• Title 2: Use {attachment} with Bookdown dependencies
• Add: usethis::use_description()
• Run lines already available in vignette
• For CI: Add install.packages("remotes"); remotes::install_deps()
• Then build your bookdown
• See examples in {gitlabr} gitlab-ci.yml.

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Some information already in vignette "bookdon-and-script.Rmd"