Caution: This package is in the verrry early stages.
library(devtools)
install_github("yutannihilation/qiitaddin")
See: https://github.com/yutannihilation/qiitr#preperation
Since no method to upload image is provided by Qiita API, this package upload images to Imgur or Gyazo. Though Imgur allows us to upload images anonymously, I recommend you to create an acount on either service, since those images uploaded without the owner cannot be deleted afterwards (as this package won't record the deletehash).
You have been warned!
If you will upload many images, I recommend Gyazo, since Imgur has some secret limit rating which you will easily hit.
After making sure that the target R Markdown file is active, click "Post to Qiita".

You can also type the command in your console.
qiitaddin::qiitaddin_knit("path/to/file.Rmd")
After knitting the document is finished, the preview window appears. Review the document and edit the following items if necessary.
coediting: A flag whether this item is co-edit mode (only available on Qiita:Team).private: A flag whether this item is private (only available on Qiita).Upload images to: Which service to upload images to. Currently, Imgur and Gyazo are supported.update an existing item: Whether to update an existing item or to create a new item.Item ID: The ID of an existing item. 
When things are done, click "Done". (If you don't set QIITA_ACCESSTOKEN environmental variable, you will be asked to provide your Qiita access token)
After that, the document is posted to Qiita and you will jump to the page.
Note that there are one important thing you have to be careful about:
Add the following code to your website.
For more information on customizing the embed code, read Embedding Snippets.