WebHelp: html validation fixes

there are some blatant html errors  in webhelp/easy-search.webdoc
http://validator.w3.org/check?uri=http%3A%2F%2Finspirehep.net%2Fhelp%2Feasy-search&charset=%28detect+automatically%29&doctype=Inline&group=0

this addresses basic compliance
T.