Add instructions for enabling folder highlight

Author: tiagofumo

README.md

@@ -32,7 +32,12 @@ let g:NERDTreeDisablePatternMatchHighlight = 1
 ```vim
 let g:NERDTreeFileExtensionHighlightFullName = 1
 let g:NERDTreeExactMatchHighlightFullName = 1
-let g:NERDTreePatternMatchHighlightFullName= 1
+let g:NERDTreePatternMatchHighlightFullName = 1
+```
+* Highlight folders using exact match
+```vim
+let g:NERDTreeHighlightFolders = 1 " enables folder icon highlighting using exact match
+let g:NERDTreeHighlightFoldersFullName = 1 " highlights the folder name
 ```
 * Customizing colors
 ```vim