add bookdown example
diff --git a/docs/bookdown_example/_book/style.css b/docs/bookdown_example/_book/style.css
new file mode 100644
index 0000000..d063c94
--- /dev/null
+++ b/docs/bookdown_example/_book/style.css
@@ -0,0 +1,14 @@
+/*!
+ * Bootstrap v3.3.7 (http://getbootstrap.com)
+ * Copyright 2011-2018 Twitter, Inc.
+ * Licensed under MIT (https://github.com/twbs/bootstrap/blob/master/LICENSE)
+ */
+
+/*!
+ * Generated using the Bootstrap Customizer (<none>)
+ * Config saved to config.json and <none>
+ *//*!
+ * Bootstrap v3.3.7 (http://getbootstrap.com)
+ * Copyright 2011-2016 Twitter, Inc.
+ * Licensed under MIT (https://github.com/twbs/bootstrap/blob/master/LICENSE)
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