Add a little info about shard option of arc_tool, a=chris

diff --git a/en-US/pages/documentation.thtml b/en-US/pages/documentation.thtml
index f4c05e6..edec05a 100755
--- a/en-US/pages/documentation.thtml
+++ b/en-US/pages/documentation.thtml
@@ -3130,8 +3130,8 @@ php arc_tool.php reindex bundle_name
 //reindex the word dictionary in bundle_name

 php arc_tool.php shard bundle_name generation
-    /* Prints information about the number of words and frequencies of words
-       within the generation'th index shard in the bundle */
+//Prints information about the number of words and frequencies of words
+// within the generation'th index shard in the bundle

 php arc_tool.php show bundle_name start num //outputs
 //items start through num from bundle_name