update intro_git to use gitlab

README.md

README.pdf

figures/config_git_rstudio.png

figures/create_ssh_key_from_rstudio.png

figures/create_ssh_key_from_rstudio_add_public_key.png

figures/create_ssh_key_from_rstudio_check_key.png

figures/create_ssh_key_from_rstudio_copy_public_key.png

figures/create_ssh_key_from_rstudio_get_public_key.png

figures/git-stages.png

figures/git-stages0.png

figures/git-stages1.png

figures/git-stages2.png

figures/git_clone_gitlab.png