vbe: Add some documentation

Add a few links to documents about Verified Boot for Embedded (VBE).
These will be expanded as development proceeds.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/develop/bootstd.rst b/doc/develop/bootstd.rst
index 5e9c0d2..dadd347 100644
--- a/doc/develop/bootstd.rst
+++ b/doc/develop/bootstd.rst
@@ -32,6 +32,7 @@
 Systems (such as Chromium OS) and devices (beyond just block and network
 devices). It supports EFI boot and EFI bootmgr too.
 
+Finally, standard boot supports the operation of :doc:`vbe`.
 
 Bootflow
 --------