Correct contexts where <p> can be used

Closes #11869.

Author: annevk

source

@@ -20722,6 +20722,7 @@ interface <dfn interface>HTMLHeadingElement</dfn> : <span>HTMLElement</span> {
    <dd><span>Palpable content</span>.</dd>
    <dt><span data-x="concept-element-contexts">Contexts in which this element can be used</span>:</dt>
    <dd>Where <span>flow content</span> is expected.</dd>
+   <dd>As a child of an <code>hgroup</code> element.</dd>
    <dt><span data-x="concept-element-content-model">Content model</span>:</dt>
    <dd><span>Phrasing content</span>.</dd>
    <dt><span data-x="concept-element-attributes">Content attributes</span>:</dt>