Add FXT dimm doc (#857)

* add document and update index

docs/index.html

@@ -254,6 +254,8 @@ h3 {border-bottom: none;}
 <li><a href="legacy/pdf/fxt_5000_series_service_guide-2018-04.pdf" target="_blank">FXT 5000 Series Field Service Guide (PDF)</a> </li>
 
 <li><a href="legacy/pdf/FXT_5K_NVRAM_Firmware_Update_Procedure_0458-009-0171_RevA.pdf" target="_blank">FXT 5000 Series NVRAM NV1604 Firmware Update Procedure (PDF)</a></li>
+
+<li><a href="legacy/pdf/fxt-dimm-replacement-0511-049-0101_RevA.pdf" target="_blank">FXT 5000 Series DIMM Replacement Procedure (PDF)</a></li>
 </ul>
 
 <h3><strong>FXT 4000 Series and Earlier </strong></h3>