`bookdown::clean_book()` should ignore `.nojekyll` file used when deployed on github pages.

[cderv]

Scenario:

• Use docs/ as output_dir
• Build the book
• Manually adds .nojekyll inside the folder (related to https://github.com/rstudio/bookdown/issues/1092 for better config)
• Push to Github
• Publish docs/ as github pages

Cleaning the project should not remove the manually created jekyll file. This could be an option in clean_book(clean = TRUE, keep_nojekyll = TRUE)

[cderv]

Using

resource_files:
  - .nojekyll

and file.create(".nojekyll") does not help.

For now, workaround is to set

file.create(bookdown:::output_path(".nojekyll"))

in a setup chunk.

So we could also offer a setup function to run for this

bookdown::use_github_pages()

that would do this

Or just export output_path and document.