1. Create Github Repository
Go to your Github account and click the big green button "New Repository", name your new repository USERNAME.github.io (for example simecek.github.io).
|New Github repo|
2. Create RStudio Project
Open RStudio, select File -> New Project -> Version Control -> Git. Copy URL address from your browser (http://github.com/USERNAME/USERNAME.github.io) into Repository URL field (see figure below). Click "Create Project" button.
|New version controlled project|
Locate the folder (USERNAME.github.io) on a disk. You will need it in the following step.
3. Select and Customize Jekyll Template
If you wish, you can use any static web page as your Github Page. For example, you can just have a redirecting script. Here, I will show how to build a simple landing page with Jekyll.
First of all, select a template you want to use, for example from http://jekyllthemes.org/.
|Jekyll Themes gallery|
Save and extract template ZIP file into your RStudio project folder USERNAME.github.io, so it should now look something like this (the folder on a disk, NOT yet Github repository).
Read extracted README file. Typically, you need to customize _config.yml and index.html files. The page itself is generated by Jekyll (ruby gem). Github supports Jekyll, so you might let generation of the actual HTML pages on him.
4. Commit Changes and Push Them to Github
Finally, go into your RStudio "Git" panel, select all files and commit them with and an appropriate message ("initial commit of my first Github Page, hurray!").
|Git panel is just next to Environment and History|
You might want to check that Github Pages are turned on in your repo's setting (https://github.com/USERNAME/USERNAME.github.io/settings). You might need to wait for a minute or two before the page is generated. Do not like it? Modify - commit - push (- make a tea - rinse - and repeat).