Update github_token.R to point Linux users to article

[rkb965]

usethis::create_github_token() returns code for calling gitcreds::gitcreds_set() to set credentials. This may not (does not?) work as a user would likely expect on Linux systems, as documented in the Managing Git(Hub) Credentials article as well as various issues. However, gitcreds::gitcreds_set() does not give any such indication, and I think a simple addition to the create_github_token() output would be valuable

git can be overwhelming, silent errors are extra challenging, the straightforward "Call `gitcreds::gitcreds_set() to register this token" sounds authoritative (leading to extra confusion when things don't work as expected), and {usethis} is such an excellent resource for getting people up and running with git. Thus, explicitly telling Linux users that they may need to reference additional documentation would likely be valuable

thanks for considering!