When working with Markdown on Github (Github flavoured markdown), I do often not see the rendered version until it is pushed to the repository. This mean that sometimes basic errors make their way and I have to make additional commits to README files etc.
You could of course use a branch!
Or! You create a gist of your Markdown file, you can actually even keep the gist private, the only drawback is images cannot be rendered if they are to follow the change going into the repository.