Add Extensions domain to sidebar (#226)

Author: oliverdunk

pages/_includes/shell.hbs

@@ -80,6 +80,7 @@
           <a href="{{{ url '/' }}}{{{ version }}}/DOMStorage" class="tot experimental">DOMStorage</a>
           <a href="{{{ url '/' }}}{{{ version }}}/Emulation" class="tot 1-2 1-3">Emulation</a>
           <a href="{{{ url '/' }}}{{{ version }}}/EventBreakpoints" class="tot experimental">EventBreakpoints</a>
+          <a href="{{{ url '/' }}}{{{ version }}}/Extensions" class="tot experimental">Extensions</a>
           <a href="{{{ url '/' }}}{{{ version }}}/FedCm" class="tot experimental">FedCm</a>
           <a href="{{{ url '/' }}}{{{ version }}}/Fetch" class="tot 1-3">Fetch</a>
           <a href="{{{ url '/' }}}{{{ version }}}/HeadlessExperimental" class="tot experimental">HeadlessExperimental</a>