title: Including external markdown file covering inline code through includeMarkdown
body: <p>I would like to include external markdown file covering inline code as well. Once I hit the Knit on RStudio, it does show only code text rather than the actual value of sys.time. If I place the content of about.md into the main.Rmd, there is no issue. The point should be related with includeMarkdown but it does not take any parameter except than path. Any suggestions ?
  Thanks in advance</p>
  
  <p><strong>main.Rmd</strong></p>
  
  <pre><code>---
  title: "test"
  author: "test"
  output: 
    flexdashboard::flex_dashboard:
      orientation: rows
      social: menu
      vertical_layout: fill
  ---
  ```{r}
    htmltools::includeMarkdown('about.md')
  ```
  </code></pre>
  
  <p><strong>about.md</strong></p>
  
  <pre><code>Today is `r format(Sys.time(), "%d %B %A %Y")`
  </code></pre>
  
  <p><strong>Current Output</strong></p>
  
  <pre><code>Today is r format(Sys.time(), "%d %B %A %Y")
  </code></pre>