Document bulk loading into rummager

This explains how to build the metasearch index in rummager from
scratch.
Fix javascript appearing before DOCTYPE

Put the javascript_include_tag and the inline script in body_end; they'd
accidentally not been put in a content block, and so were appearing
outside the content at the top of the HTTP response.

Remove the duplicate javascript_include_tag from head.
Merge pull request #14 from alphagov/fix_top_of_page_javascript

Fix javascript appearing before DOCTYPE
Merge pull request #13 from alphagov/document_bulk_load

Document bulk loading into rummager