raw.githubusercontent.com/username/repo-name/branch-name/path
Replace username
with the username of the user that created the repo.
Replace repo-name
with the name of the repo.
Replace branch-name
with the name of the branch.
Replace path
with the path to the file.
To reverse to go to GitHub.com:
GitHub.com/username/repo-name/directory-path/blob/branch-name/filename