docs: Update files for renesas-ra port.

Signed-off-by: Takeo Takahashi <takeo.takahashi.xv@renesas.com>

docs/index.rst

@@ -16,3 +16,4 @@ MicroPython documentation and references
     wipy/quickref.rst
     unix/quickref.rst
     zephyr/quickref.rst
+    renesas-ra/quickref.rst

docs/templates/topindex.html

@@ -78,6 +78,10 @@
         <a class="biglink" href="{{ pathto("zephyr/quickref") }}">Quick reference for the Zephyr port</a><br/>
         <span class="linkdescr">snippets of useful code and a tutorial</span>
       </p>
+      <p class="biglink">
+        <a class="biglink" href="{{ pathto("renesas-ra/quickref") }}">Quick reference for the Renesas RA</a><br/>
+        <span class="linkdescr">general information for Renesas RA based boards, snippets of useful code, and a tutorial</span>
+      </p>
     </td>
   </tr></table>