add render method

lib/DB/PlaceholderPost.rakumod

@@ -12,6 +12,9 @@ unit class PlaceholderPost does Post is json(:pretty);
 #| cheaty way
 has Bool:D $.placeholder = True;
 
+#| An optional body for the placeholder post
+has Str $.body;
+
 method title(--> Str:D) {
     "Placeholder Article"
 }
@@ -30,3 +33,8 @@ method empty(--> PlaceholderPost:D) {
 method all-slugs(--> Array[Str:D]) {
     Array[Str:D].new
 }
+
+# Return the body if there is one, the empty string if there isn't one
+method render-html(--> Str:D) {
+    $!body // ''
+}