Add latest release to homepage.

content/_index.html

 ---
 description: Secure messaging, anywhere
 title: Secure messaging, anywhere
+releaseVersion: 1.2.16
+releaseDate: 27 February 2021
 ---
 <div class="intro">
   <ul id="introlist">

themes/briar/layouts/_default/list.html

 {{ define "main" }}
 <h2>{{ with .Title }} {{ . }} {{ else }} {{ .Site.Title }} {{ end }}</h2>
+<p><strong>Latest Release:</strong> Briar {{ .Params.releaseVersion }} ({{ .Params.releaseDate }})</p>
 <p><strong>Latest News:</strong>
 {{ range first 1 (where .Site.RegularPages "Section" "news").ByDate.Reverse }}
  <a href="{{.Permalink}}">{{.Title}}</a>