Add markdown to DESCRIPTION to fix vignette not building error

Jakub Sobolewski · Jakub Sobolewski · commit 5360c23f1671 · 2021-11-18T10:40:11.000+01:00
Solution based on discussion in yihui/knitr#1864
diff --git a/DESCRIPTION b/DESCRIPTION
@@ -26,7 +26,8 @@ Suggests:
     shinydashboard,
     covr,
     knitr,
-    rmarkdown
+    rmarkdown,
+    markdown
 RoxygenNote: 7.1.2
 VignetteBuilder:
     knitr
