Editorial: add missing word (#542)

closes #541

Author: scottaohara

index.html

@@ -1589,7 +1589,7 @@ <h2 id="docconformance">
               </div>
             </th>
             <td>
-              If the `img` has non-empty [^img/alt^] (`alt="some text"`) or an accessible name is provided another 
+              If the `img` has non-empty [^img/alt^] (`alt="some text"`) or an accessible name is provided by another 
               <a data-cite="html-aam-1.0#img-element-accessible-name-computation">`img` naming method</a>, 
               or the `img` has no `alt` and has not been provided a name:<br>
               <code>role=<a href="#index-aria-img">img or image</a></code>