move table to code block

as it doesn't render properly in https://www.ietf.org/archive/id/draft-ietf-cellar-ffv1-v4-18.html#name-frame-2

Author: dericed

ffv1.md

@@ -1371,33 +1371,35 @@ Frame( NumBytes ) {                                           |
 
 The following is an architecture overview of Slices in a Frame:
 
-+-----------------------------------------------------------------+
+```
++---------------------------------------------------------------+
 | first Slice header                                            |
-+-----------------------------------------------------------------+
++---------------------------------------------------------------+
 | first Slice content                                           |
-+-----------------------------------------------------------------+
++---------------------------------------------------------------+
 | first Slice footer                                            |
-+-----------------------------------------------------------------+
-|---------------------------------------------------------------|
-+-----------------------------------------------------------------+
++---------------------------------------------------------------+
+| ------------------------------------------------------------- |
++---------------------------------------------------------------+
 | second Slice header                                           |
-+-----------------------------------------------------------------+
++---------------------------------------------------------------+
 | second Slice content                                          |
-+-----------------------------------------------------------------+
++---------------------------------------------------------------+
 | second Slice footer                                           |
-+-----------------------------------------------------------------+
-|---------------------------------------------------------------|
-+-----------------------------------------------------------------+
++---------------------------------------------------------------+
+| ------------------------------------------------------------- |
++---------------------------------------------------------------+
 | ...                                                           |
-+-----------------------------------------------------------------+
-|---------------------------------------------------------------|
-+-----------------------------------------------------------------+
++---------------------------------------------------------------+
+| ------------------------------------------------------------- |
++---------------------------------------------------------------+
 | last Slice header                                             |
-+-----------------------------------------------------------------+
++---------------------------------------------------------------+
 | last Slice content                                            |
-+-----------------------------------------------------------------+
-| last Slice footer                                               |
-+-----------------------------------------------------------------+
++---------------------------------------------------------------+
+| last Slice footer                                             |
++---------------------------------------------------------------+
+```
 
 ## Slice