add bookmarks and press help documentation

doc/NERD_tree.txt

@@ -642,6 +642,12 @@ NERD tree. These options should be set in your vimrc.
 |'NERDTreeWinSize'|             Sets the window size when the NERD tree is
                                 opened.
 
+|'NERDTreeBmarksLabel'|         Enables display of the Bookmarks label in
+                                the NERD tree.
+
+|'NERDTreePressHelp'|           Enables display of the 'Press ? for help' at
+                                the top of the NERD tree.
+
 ------------------------------------------------------------------------------
 3.2. Customisation details                             *NERDTreeOptionDetails*
 
@@ -921,6 +927,28 @@ Default: 31.
 
 This option is used to change the size of the NERD tree when it is loaded.
 
+------------------------------------------------------------------------------
+                                                       *'NERDTreeBmarksLabel'*
+Values: 0 or 1
+Default: 1
+
+This options enables the 'Bookmarks' label. Use one of the following lines
+to set this option: >
+    let NERDTreeBmarksLabel=0
+    let NERDTreeBmarksLabel=1
+<
+
+------------------------------------------------------------------------------
+                                                         *'NERDTreePressHelp'*
+Values: 0 or 1
+Default: 1
+
+This options enables the 'Press ? for help' text. Use one of the following
+lines to set this option: >
+    let NERDTreePressHelp=0
+    let NERDTreePressHelp=1
+<
+
 ==============================================================================
 4. The NERD tree API                                             *NERDTreeAPI*