I wanted to create a read-only template for future posts on this site (I’m using jekyll because of github pages integration).
Using the terminal, I use iTerm2 because it is the dog’s bollocks, type:
chmod 0444 /path/to/file/file.md
e.g. in my case I have done this for this site
chmod 0444 _posts/2014-01-01-READ_ONLY.md
so when I create a new post I have a starting point.