Add strikethrough text-decoration example

Author: Lachlan Campbell

docs/typography/text-decoration/index.html

@@ -85,6 +85,8 @@ <h3 class="f5 fw4 pt4 ttu tracked">Text Decoration Underline</h3>
       vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren,
       no sea takimata sanctus est Lorem ipsum dolor sit amet.
       </p>
+        <h3 class="f5 fw4 pt4 ttu tracked">Text Decoration Strikethrough</h3>
+        <p class="strike">Lorem ipsum dolor sit amet</p>
         <div class="mt5 cf">
           <div class="dib mr4">
             <h1 class="f4 ttu tracked fw6">Previous</h1>

src/templates/docs/text-decoration/index.html

@@ -49,6 +49,8 @@ <h3 class="f5 fw4 pt4 ttu tracked">Text Decoration Underline</h3>
       vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren,
       no sea takimata sanctus est Lorem ipsum dolor sit amet.
       </p>
+        <h3 class="f5 fw4 pt4 ttu tracked">Text Decoration Strikethrough</h3>
+        <p class="strike">Lorem ipsum dolor sit amet</p>
         <div class="mt5 cf">
           <div class="dib mr4">
             <h1 class="f4 ttu tracked fw6">Previous</h1>