Documentation: Add x86 bootblock support

Document what is involved with adding the bootblock support.

TEST=None

Change-Id: I6c8cc38e1b9346b4962588b33ca5e4ab8eac24c3
Signed-off-by: Lee Leahy <leroy.p.leahy@intel.com>
Reviewed-on: https://review.coreboot.org/13441
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

Documentation/Intel/development.html

@@ -69,6 +69,7 @@
   </li>
   <li>Get result to start <a target="_blank" href="SoC/soc.html#Descriptor">booting</a></li>
   <li><a target="_blank" href="SoC/soc.html#EarlyDebug">Early Debug</a></li>
+  <li>Implement and debug the <a target="_blank" href="SoC/soc.html#Bootblock">bootblock</a> code</li>
 </ol>