Update docs

usage.html

@@ -4,7 +4,7 @@
   <meta charset="utf-8" /><meta name="generator" content="Docutils 0.17.1: http://docutils.sourceforge.net/" />
 
   <meta name="viewport" content="width=device-width, initial-scale=1.0" />
-  <title>Using parsedmarc &mdash; parsedmarc 8.6.3 documentation</title>
+  <title>Using parsedmarc &mdash; parsedmarc 8.6.4 documentation</title>
       <link rel="stylesheet" href="_static/pygments.css" type="text/css" />
       <link rel="stylesheet" href="_static/css/theme.css" type="text/css" />
   <!--[if lt IE 9]>
@@ -36,7 +36,7 @@
             parsedmarc
           </a>
               <div class="version">
-                8.6.3
+                8.6.4
               </div>
 <div role="search">
   <form id="rtd-search-form" class="wy-form" action="search.html" method="get">
@@ -193,7 +193,7 @@ Elasticsearch, Splunk and/or S3</p></li>
 Elasticsearch, Splunk and/or S3</p></li>
 <li><p><code class="docutils literal notranslate"><span class="pre">strip_attachment_payloads</span></code> - bool: Remove attachment
 payloads from results</p></li>
-<li><p><code class="docutils literal notranslate"><span class="pre">output</span></code> - str: Directory to place JSON and CSV files in</p></li>
+<li><p><code class="docutils literal notranslate"><span class="pre">output</span></code> - str: Directory to place JSON and CSV files in.  This is required if you set either of the JSON output file options.</p></li>
 <li><p><code class="docutils literal notranslate"><span class="pre">aggregate_json_filename</span></code> - str: filename for the aggregate
 JSON output file</p></li>
 <li><p><code class="docutils literal notranslate"><span class="pre">forensic_json_filename</span></code> - str: filename for the forensic