Add section headers.

README.markdown

@@ -13,6 +13,8 @@ installing from this repository, add the following to your vimrc:
 
 ## Configuration
 
+### Fenced Codeblock Highlighting
+
 To enable fenced code block syntax highlighting in your markdown
 documents, add the following to your `.vimrc`:
 
@@ -20,10 +22,14 @@ documents, add the following to your `.vimrc`:
 
 **Note**: The fenced language names must be valid names of syntax files in vim's `syntax` folder. For example: `syntax/ruby.vim`.
 
+### Syntax Concealment
+
 To disable markdown syntax concealing, add the following to your `.vimrc`:
 
     let g:markdown_syntax_conceal = 0
 
+### Highlighting Synchronization
+
 Syntax highlighting is synchronized in 50 lines. This may cause collapsed
 highlighting on large fenced code blocks.
 In that case, set `g:markdown_minlines` to a larger value in your `.vimrc`:
@@ -32,6 +38,8 @@ In that case, set `g:markdown_minlines` to a larger value in your `.vimrc`:
 
 **Note**: Setting `g:markdown_minlines` to a value that is too large value may cause poor highlighting performance.
 
+### Folding
+
 To enable folding, add the following to your `.vimrc`:
 
     let g:markdown_folding = 1