Set up static html documentation for R package

[terrytangyuan]

We need to scaffold R package documentation website. pkgdown is a popular choice in R community to generate this automatically through simple configuration. We should at least scaffold the following pages:

• API reference
• Tutorials
• Index page

[terrytangyuan]

FYI I'll be working on this soon. Also cc @missaugustina since you are working on docs in #227 and just realized that you are involved in the R world as well. I don't think there will be conflict with Python docs though since it's totally independent.

[missaugustina]

I actually use Rstudio's Tensorflow/Keras libs so yeah I can definitely help here. (edited) I just noticed the R-package directory at the parent level of this repo. What's the vision for Tensorflow IO as an R-package? Would you or could you recommend someone to do a quick hangouts call with me for a high level tour of the repo since I'm so new to this project?

[terrytangyuan]

@missaugustina The R package we took for tfio is actually the same as what we did for the other TensorFlow R packages, through reticulate package. I believe the code structure would be easier to understand once you get familiar with reticulate. The R package consists of thin wrappers of the Python API. We are definitely lack of documentations and examples though.

[missaugustina]

I'm familiar with using reticulate but haven't poked under the hood except when debugging. Do you have an idea of what examples you would want or would figuring that out also be part of the example documentation task?

[terrytangyuan]

@missaugustina An example to start with would be using it together with keras R package and tfdatasets package. Examples for different types of datasets would be useful too.