Broke up R documentation and moved GPU page

Separated R page into 2 pages (running jobs and installing packages - Issue #31 (closed))

Moved how to run GPU jobs from app specific guides to parent folder (submitting jobs).

content/applications/user_software/r_packages.md

++++
+title = "Using R Libraries"
+description =  "How to install R packages on HCC resources."
++++
+
+Many commonly used R packages are included in the base R installation available on HCC clusters,
+ such as `tidyverse` and `stringr`. However, users are able to install other packages in their 
+user libraries.
+
+- [Adding packages](#adding-packages)
+  - [Installing packages interactively](#installing-packages-interactively)
+  - [Installing packages using R CMD INSTALL](#installing-packages-using-r-cmd-install)
+
+  
+### Adding packages
+
+There are two options to install packages. The first is to run R on the
+login node and run R interactively to install packages. The second is to
+use the `R CMD INSTALL` command.
+
+{{% notice info %}}
+All R packages must be installed from the login node. R libraries are
+stored in user's home directories which are not writable from the worker
+nodes.
+{{% /notice %}}
+
+#### Installing packages interactively
+
+1.  Load the R module with the command `module load R`
+    -  Note that each version of R uses its own user libraries. To
+       install packages under a specific version of R, specify which
+       version by using the module load command followed by the version
+       number. For example, to load R version 3.5, you would use the
+       command `module load R/3.5`
+2.  Run R interactively using the command `R`
+3.  From within R, use the `install.packages()` command to install
+    desired packages. For example, to install the package `ggplot2`
+    use the command `install.packages("ggplot2")`
+
+Some R packages, require external compilers or additional libraries. If
+you see an error when installing your package you might need to load
+additional modules to make these compilers or libraries available. For
+more information about this, refer to the package documentation.
+
+#### Installing packages using R CMD INSTALL
+
+To install packages using `R CMD INSTALL` the zipped package must
+already be downloaded to the cluster. You can download package source
+using `wget`. Then the `R CMD INSTALL` command can be used when
+pointed to the full path of the source tar file. For example, to install
+ggplot2 the following commands are used:
+
+{{< highlight bash >}}
+# Download the package source:
+wget https://cran.r-project.org/src/contrib/ggplot2_3.2.1.tar.gz
+
+# Install the package:
+R CMD INSTALL ./ggplot2_2.2.1.tar.gz
+{{< /highlight >}}
+
+Additional information on using the `R CMD INSTALL` command can be
+found in the R documentation which can be seen by typing `?INSTALL`
+within the R console.