title: add image in title page of rmarkdown pdf
body: <p>I am attempting to create an rmarkdown document. I have finally figured out a way to approach this, although it has taken quite some time. The last thing I would like to be able to do is to add an image to the title page of my pdf document. </p>
  
  <p>The trouble I have is that my title page is defined by the top section of YAML. Below is the contents of my <code>example.Rmd</code> file. I use the Knit PDF button in RStudio to turn it into a PDF.</p>
  
  <pre><code>---
  title: "This is a my document"
  author: "Prepared by: Dan Wilson"
  date: '`r paste("Date:",Sys.Date())`'
  mainfont: Roboto Light
  fontsize: 12pt
  documentclass: report
  output: 
    pdf_document:
      latex_engine: xelatex
      highlight: tango
  ---
  This is an R Markdown document. Markdown is a simple formatting syntax for authoring HTML, PDF, and MS Word documents. For more details on using R Markdown see &lt;http://rmarkdown.rstudio.com&gt;.
  
  When you click the **Knit** button a document will be generated that includes both content as well as the output of any embedded R code chunks within the document. You can embed an R code chunk like this:
  
  ```{r}
  summary(cars)
  ```
  
  You can also embed plots, for example:
  
  ```{r, echo=FALSE}
  plot(cars)
  ```
  
  Note that the `echo = FALSE` parameter was added to the code chunk to prevent printing of the R code that generated the plot.
  </code></pre>
  
  <p>If anyone has some tips that would allow me to put an image (logo.png) above my title that would be great.</p>