Add new widths docs.

Author: mrmrs

docs/layout/widths/index.html

@@ -164,6 +164,9 @@ <h3 class="f5 book pt4 caps">Width Percentages</h3>
           <div class="w-33 bg-black-10 mb2">
             <code class="code">w-33</code>
           </div>
+          <div class="w-third bg-black-10 mb2">
+            <code class="code">w-third</code>
+          </div>
           <div class="w-34 bg-black-10 mb2">
             <code class="code">w-34</code>
           </div>

src/templates/docs/widths/index.html

@@ -121,6 +121,9 @@ <h3 class="f5 book pt4 caps">Width Percentages</h3>
           <div class="w-33 bg-black-10 mb2">
             <code class="code">w-33</code>
           </div>
+          <div class="w-third bg-black-10 mb2">
+            <code class="code">w-third</code>
+          </div>
           <div class="w-34 bg-black-10 mb2">
             <code class="code">w-34</code>
           </div>