Migrate documentation to roxygen2md

Change-Id: If5370cd207770f3e05c6f5cd063bd2a414b92bcb
diff --git a/DESCRIPTION b/DESCRIPTION
index 06285a6..3b8f051 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -62,6 +62,8 @@
     'ci.R'
     'collocationAnalysis.R'
     'collocationScoreQuery.R'
-    'highcharter-helper.R'
+    'hc_add_onclick_korap_search.R'
+    'hc_freq_by_year_ci.R'
     'misc.R'
     'reexports.R'
+Roxygen: list(markdown = TRUE)