Add missing rmarkdown import in recursive CA demo

Change-Id: If0b4e9863d2d48565b3bcef4fb500d9cdceafa61
diff --git a/demo/recursiveCA.R b/demo/recursiveCA.R
index 1cff680..0f2d104 100644
--- a/demo/recursiveCA.R
+++ b/demo/recursiveCA.R
@@ -1,6 +1,7 @@
 library(RKorAPClient)
 library(tidyverse)
 library(knitr)
+library(rmarkdown)
 
 nodeWordform <- 'aufmerksam'
 mdFile <- tempfile(nodeWordform, fileext = ".md")