message: Improve code highlighting
diff: @@ -57,12 +57,12 @@ be able to find the correct path to the module.
  Once the `tensorflow-io` Python package has beem successfully installed, you
  can then install the latest stable release of the R package via:
  -```
  +```r
  install.packages('tfio')
  ```
  You can also install the development version from Github via:
  -```
  +```r
  if (!require("devtools")) install.packages("devtools")
  devtools::install_github("tensorflow/io", subdir = "R-package")
  ```
  @@ -89,7 +89,7 @@ A package file `artifacts/tensorflow_io-*.whl` will be generated after a build i
  We provide a reference Dockerfile [here](R-package/scripts/Dockerfile) for you
  so that you can use the R package directly for testing. You can build it via:
  -```
  +```sh
  docker build -t tfio-r-dev -f R-package/scripts/Dockerfile .
  ```
  @@ -97,7 +97,7 @@ Inside the container, you can start your R session, instantiate a `SequenceFileD
  from an example [Hadoop SequenceFile](https://wiki.apache.org/hadoop/SequenceFile)
  [string.seq](R-package/tests/testthat/testdata/string.seq), and then use any [transformation functions](https://tensorflow.rstudio.com/tools/tfdatasets/articles/introduction.html#transformations) provided by [tfdatasets package](https://tensorflow.rstudio.com/tools/tfdatasets/) on the dataset like the following:
  -```{R}
  +```r
  library(tfio)
  dataset <- sequence_file_dataset("R-package/tests/testthat/testdata/string.seq") %>%
  dataset_repeat(2)
  