Update vimdoc with fat_tables addition

Author: MeanderingProgrammer

doc/render-markdown.txt

@@ -96,6 +96,7 @@ modified by the user.
             (block_quote (block_quote_marker) @quote_marker)
             (block_quote (paragraph (inline (block_continuation) @quote_marker)))
 
+            (pipe_table) @table
             (pipe_table_header) @table_head
             (pipe_table_delimiter_row) @table_delim
             (pipe_table_row) @table_row
@@ -122,6 +123,8 @@ modified by the user.
             -- conceallevel used for buffer when being rendered
             rendered = 3,
         },
+        -- Add a line above and below tables to complete look, ends up like a window
+        fat_tables = true,
         -- Define the highlight groups to use when rendering various components
         highlights = {
             heading = {