Improve comment for url_placeholders method

lib/jekyll/page.rb

@@ -73,7 +73,8 @@ module Jekyll
       }).to_s
     end
 
-    # See url.rb for an explanation
+    # Returns a hash of URL placeholder names (as symbols) mapping to the
+    # desired placeholder replacements. For details see "url.rb"
     def url_placeholders
       {
         :path       => @dir,

lib/jekyll/post.rb

@@ -205,7 +205,8 @@ module Jekyll
       }).to_s
     end
 
-    # See url.rb for an explanation
+    # Returns a hash of URL placeholder names (as symbols) mapping to the
+    # desired placeholder replacements. For details see "url.rb"
     def url_placeholders
       {
         :year        => date.strftime("%Y"),