title: Including citation and references when using appendix on RMarkdown
body: <p>I am working on <code>RMarkdown</code> to generate a report that includes an appendix after references. I have written the appendix on a different <code>RMarkdown</code> file and adapted my principal file to compile it. This is the code for my principal Rmd file that generates report:</p>
  
  <pre><code>---
  bibliography: bb.bib
  fontsize: 11pt
  nocite: '@*'
  output: 
    pdf_document:
      includes:
        after_body: Demo2.Rmd
        keep_tex: yes
  link-citations: true
  ---
  \newpage
  
  \section{Testing}\label{sec1}
  ```{r}
  summary(cars)
  ```
  \section{Demo}
  This was done using @shiina and we will use some info from Section \ref{sec1} to do.
  ```{r}
  summary(iris[,1:2])
  ```
  \section{References} 
  </code></pre>
  
  <p>The file <code>bb.bib</code> contains next references:</p>
  
  <pre><code>@article {shiina,
  author = {Shiina, Takayuki and Birge, John R.},
  title = {Stochastic unit commitment problem},
  journal = {International Transactions in Operational Research},
  volume = {11},
  number = {1},
  publisher = {Blackwell Publishing},
  pages = {19--32},
  year = {2004},
  }
  
  @book{groewe2001,
    title={Stochastic unit commitment in hydro-thermal power production planning},
    author={Gr{\"o}we-Kuska, N. and R{\"o}misch, W.},
    year={2001},
    series = { Preprints aus dem Institut f{\"u}r Mathematik },
    publisher = { Humboldt-Universit{\"a}t zu Berlin, Institut f{\"u}r Mathematik },
  }
  </code></pre>
  
  <p>Finally, my appendix Rmd file, <code>Demo2.Rmd</code>, contains this structure:</p>
  
  <pre><code>\appendix
  \section*{Appendix}
  \section{Additional info}
  In this section we also follow @shiina to explain concepts.
  </code></pre>
  
  <p>Compilation works fine and generate document but issues are appearing in the appendix section. I used a reference with <code>@shiina</code> to cite something, but I am getting this output in the final report:
  <a href="https://i.stack.imgur.com/dKGAI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/dKGAI.png" alt="enter image description here"></a></p>
  
  <p>The circle in black shows that citation from bibliography is not working. Instead of <code>@shiina</code>, it should appear <code>Shiina and Birge (2004)</code>. I have tried replacing Rmd file with a TeX file but it did not work.</p>
  
  <p>Is it any way to correct that?, I do not know if <code>after_body</code> needs to be adjusted or what to do. </p>