Update R version documentation

docs/source/config_files.rst

@@ -212,7 +212,7 @@ If you only need to run things once during the build phase use :ref:`postBuild`.
 
 Sometimes you want to specify the version of the runtime
 (e.g. the version of Python or R),
-but the environment specification format don't let you specify this information
+but the environment specification format will not let you specify this information
 (e.g. requirements.txt or install.R).
 For these cases, we have a special file, ``runtime.txt``.
 
@@ -220,7 +220,7 @@ For these cases, we have a special file, ``runtime.txt``.
 
    ``runtime.txt`` is only supported when used with environment specifications
    that do not already support specifying the runtime
-   (e.g. when using ``environment.yml`` for conda or ``Project.toml`` for Julia,
+   (when using ``environment.yml`` for conda or ``Project.toml`` for Julia,
    ``runtime.txt`` will be ignored).
 
 To use python-2.7: add ``python-2.7`` in runtime.txt file.
@@ -231,8 +231,11 @@ Python 2 installed. To see a full example repository, visit our
 repo2docker uses R libraries pinned to a specific snapshot on
 `MRAN <https://mran.microsoft.com/documents/rro/reproducibility>`_.
 You need to have a ``runtime.txt`` file that is formatted as
-``r-<YYYY>-<MM>-<DD>``, where YYYY-MM-DD is a snapshot at MRAN that will be
-used for installing libraries.
+``r-<RVERSION>-<YYYY>-<MM>-<DD>``, where YYYY-MM-DD is a snapshot at MRAN that will be
+used for installing libraries. You can set RVERSION to 3.4, 3.5 or 3.6 to select
+the version of R you want to use. If you do not specify a R version the latest
+released version will be used (currently R 3.6). You can also specify the exact
+patch release you want to use for the 3.5 and 3.6 series.
 
 To see an example R repository, visit our `R
 example in binder-examples <https://github.com/binder-examples/r/blob/master/runtime.txt>`_.

docs/source/faq.rst

@@ -49,10 +49,11 @@ Julia versions 0.6.x and earlier are supported via a :ref:`REQUIRE <REQUIRE>` fi
 R
 ~
 
-Only R 3.4.4 is currently supported, which is installed via ``apt`` from the
-`ubuntu bionic repository <https://packages.ubuntu.com/bionic/r-base>`_.
-
+The default version of R is currently R 3.6.1. You can select the version of
+R you want to use by specifying it in the :ref:`runtime.txt <runtime.txt>`
+file.
 
+We support R versions 3.4, 3.5 and 3.6.
 
 
 Why is my repository is failing to build with ``ResolvePackageNotFound`` ?
@@ -149,17 +150,17 @@ notebooks (among others).
     the container, use the ``--volumes`` option instead. Similarly,
     for a fully customized user Dockerfile, this option is not
     guaranteed to work.
-    
-    
+
+
 Why is my R shiny app not launching?
 ----------------------------------------------------------------------------------
 
 If you are trying to run an R shiny app using the ``/shiny/folder_containing_shiny``
 url option, but the launch returns "The application exited during initialization.",
 there might be something wrong with the specification of the app. One way of debugging
-the app in the container is by running the ``rstudio`` url, open either the ui or 
-server file for the app, and run the app in the container rstudio. This way you can 
-see the rstudio logs as it tries to initialise the shiny app. If you a missing a 
+the app in the container is by running the ``rstudio`` url, open either the ui or
+server file for the app, and run the app in the container rstudio. This way you can
+see the rstudio logs as it tries to initialise the shiny app. If you a missing a
 package or other dependency for the container, this will be obvious at this stage.