The template.yaml file here is for a rmarkdown template. This file are used by rmarkdown::draft to create a new file from template or by RStudio File > New File > R markdown... > From Template. To be able to list all templates available, RStudio read through each template.yaml found in packages present in the library. Base on the metadata found, the template can be rendered in RStudio IDE.
Documentation for template is here
The yaml is read by RStudio using yaml::yaml.load_file that calls readLines - the function responsible for the warning.
Standard yaml for template should be:
name: name to print in RStudio IDE
description: >
Description when mouse is above the template
create_dir: false
(create_dir is for enforcing the creation of a new directory when creating the template (see help("draft", "rmarkdown"))
the template.yaml file from the raw
seems to have an incomplete final line (no EOL marker). This should be fix for this package but I can't find the source on github.