add doc for bookmarks

doc/NERD_tree.txt

@@ -22,7 +22,9 @@ CONTENTS                                                   *NERDTree-contents*
     1.Intro...................................|NERDTree|
     2.Functionality provided..................|NERDTreeFunctionality|
         2.1 Global commands...................|NERDTreeGlobalCommands|
-        2.2 Bookmark commands.................|NERDTreeBookmarkCommands|
+        2.2 Bookmarks.........................|NERDTreeBookmarks|
+            2.2.1 The bookmark table..........|NERDTreeBookmarkTable|
+            2.2.2 Bookmark commands...........|NERDTreeBookmarkCommands|
         2.3 NERD tree mappings................|NERDTreeMappings|
         2.4 The filesystem menu...............|NERDTreeFilesysMenu|
     3.Options.................................|NERDTreeOptions|
@@ -110,11 +112,20 @@ The following features and functionality are provided by the NERD tree:
     Close the NERD tree in this tab.
 
 ------------------------------------------------------------------------------
-2.2. Bookmark Commands                              *NERDTreeBookmarkCommands*
+2.2. Bookmarks                                             *NERDTreeBookmarks*
 
 Bookmarks in the NERD tree are a way to tag files or directories of interest.
 For example, you could use bookmarks to tag all of your project directories.
-See also |:NERDTree| and |:NERDTreeFromBookmark|.
+
+------------------------------------------------------------------------------
+2.2.1. The Bookmark Table                              *NERDTreeBookmarkTable*
+
+If the bookmark table is active (see |NERDTree-B| and
+|NERDTreeShowBookmarks|), it will be rendered above the tree. You can double
+click bookmarks or use the |NERDTree-o| mapping to activate them.
+
+------------------------------------------------------------------------------
+2.2.2. Bookmark commands                            *NERDTreeBookmarkCommands*
 
 Note that the following commands are only available in the NERD tree buffer.
 
@@ -147,13 +158,15 @@ Note that the following commands are only available in the NERD tree buffer.
 :ClearAllBookmarks
     Remove all bookmarks.
 
+See also |:NERDTree| and |:NERDTreeFromBookmark|.
+
 ------------------------------------------------------------------------------
 2.3. NERD tree Mappings                                     *NERDTreeMappings*
 
 Default  Description~                                             help-tag~
 Key~
 
-o.......Open selected file, or expand selected dir...............|NERDTree-o|
+o.......Open files, directories and bookmarks....................|NERDTree-o|
 go......Open selected file, but leave cursor in the NERDTree.....|NERDTree-go|
 t.......Open selected node in a new tab..........................|NERDTree-t|
 T.......Same as 't' but keep the focus on the current tab........|NERDTree-T|
@@ -187,6 +200,7 @@ cd......Change the CWD to the dir of the selected node...........|NERDTree-cd|
 H.......Toggle whether hidden files displayed....................|NERDTree-H|
 f.......Toggle whether the file filters are used.................|NERDTree-f|
 F.......Toggle whether files are displayed.......................|NERDTree-F|
+B.......Toggle whether the bookmark table is displayed...........|NERDTree-B|
 
 q.......Close the NERDTree window................................|NERDTree-q|
 ?.......Toggle the display of the quick help.....................|NERDTree-?|
@@ -197,8 +211,16 @@ Default key: o
 Map option: NERDTreeMapActivateNode
 Applies to: files and directories.
 
-If a file node is selected, it is opened in the previous window. If a
+If a file node is selected, it is opened in the previous window.
-directory is selected it is opened or closed depending on its current state.
+
+If a directory is selected it is opened or closed depending on its current
+state.
+
+If a bookmark that links to a directory is selected then that directory
+becomes the new root.
+
+If a bookmark that links to a file is selected then that file is opened in the
+previous window.
 
 ------------------------------------------------------------------------------
                                                                  *NERDTree-go*
@@ -431,6 +453,14 @@ Applies to: no restrictions.
 
 Toggles whether file nodes are displayed.
 
+------------------------------------------------------------------------------
+                                                                  *NERDTree-B*
+Default key: B
+Map option: NERDTreeMapToggleBookmarks
+Applies to: no restrictions.
+
+Toggles whether the bookmarks table is displayed.
+
 ------------------------------------------------------------------------------
                                                                   *NERDTree-q*
 Default key: q
@@ -525,6 +555,9 @@ NERD tree. These options should be set in your vimrc.
 
 |NERDTreeQuitOnOpen|            Closes the tree window after opening a file.
 
+|NERDTreeShowBookmarks|         Tells the NERD tree whether to display the
+                                bookmarks table on startup.
+
 |NERDTreeShowFiles|             Tells the NERD tree whether to display files
                                 in the tree on startup.
 
@@ -704,6 +737,15 @@ Default: 0
 If set to 1, the NERD tree window will close after opening a file with the
 |NERDTree-o| or |NERDTree-tab| mappings.
 
+------------------------------------------------------------------------------
+                                                       *NERDTreeShowBookmarks*
+Values: 0 or 1.
+Default: 0.
+
+If this option is set to 1 then the bookmarks table will be displayed.
+
+This option can be toggled dynamically with the |NERDTree-B| mapping.
+
 ------------------------------------------------------------------------------
                                                            *NERDTreeShowFiles*
 Values: 0 or 1.