add bookdown example
diff --git a/docs/bookdown_example/packages.bib b/docs/bookdown_example/packages.bib
new file mode 100644
index 0000000..0859697
--- /dev/null
+++ b/docs/bookdown_example/packages.bib
@@ -0,0 +1,29 @@
+@Manual{R-base,
+ title = {R: A Language and Environment for Statistical Computing},
+ author = {{R Core Team}},
+ organization = {R Foundation for Statistical Computing},
+ address = {Vienna, Austria},
+ year = {2018},
+ url = {https://www.R-project.org/},
+}
+@Manual{R-bookdown,
+ title = {bookdown: Authoring Books and Technical Documents with R Markdown},
+ author = {Yihui Xie},
+ note = {R package version 0.7.19},
+ url = {https://github.com/rstudio/bookdown},
+ year = {2018},
+}
+@Manual{R-knitr,
+ title = {knitr: A General-Purpose Package for Dynamic Report Generation in R},
+ author = {Yihui Xie},
+ year = {2018},
+ note = {R package version 1.20},
+ url = {https://CRAN.R-project.org/package=knitr},
+}
+@Manual{R-rmarkdown,
+ title = {rmarkdown: Dynamic Documents for R},
+ author = {JJ Allaire and Yihui Xie and Jonathan McPherson and Javier Luraschi and Kevin Ushey and Aron Atkins and Hadley Wickham and Joe Cheng and Winston Chang},
+ year = {2018},
+ note = {R package version 1.10},
+ url = {https://CRAN.R-project.org/package=rmarkdown},
+}