The steps in the helpful links others have given you are based on need to render an Rmd file to some format (I think). So if that's what you need to do, follow those steps.
However, if you have a document that doesn't need rendering, the main step you need is the "put it in the static directory" step. You can then refer to that file in your blog via the file path.
Here's an example. I have a subdirectory called "pdf" in my static folder where I store PDF documents I want to link to on my website. If I have a file named "file1.pdf" I can insert a link to it via markdown syntax like:
See the [handout](/pdf/file1.pdf) for more info. Note the path starts with a forward slash, which is key.
Also see this github comment, which I think makes this all clearer than I just did.