Add posterdown_betterland

better poster design for posterdown users.
diff --git a/NAMESPACE b/NAMESPACE
index 1284ebc..1f7e92e 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -1,5 +1,6 @@
 # Generated by roxygen2: do not edit by hand
 
+export(posterdown_betterland)
 export(posterdown_html)
 export(posterdown_latex)
 export(posterdown_pdf)