Add: Completion for todo.txt

Intelligent complete for context and projects, try it ;)

doc/todo.txt

@@ -31,7 +31,7 @@ COMMANDS                                                       *todo-commands*
 
 `date<tab>`  : (Insert mode) Insert the current date
 
-`<LocalLeader>-x` : Toggle mark task as done (inserts or remove current date as 
+`<LocalLeader>-x` : Toggle mark task as done (inserts or remove current date as
                     completion date)
 
 `<LocalLeader>-X` : Mark all tasks as completed
@@ -56,3 +56,28 @@ g:Todo_txt_second_level_sort_mode="i"
 
 
 For more information on the available flags see help :sort
+
+We also provide a nice complete function for project and context, to use it
+add the following lines to your vimrc:
+
+" Use TodoComplete as the user complete
+au filetype todo setlocal completefunc=TodoComplete
+
+You can also start automatically the completion when entering '+' or '@' by
+adding the next lines to your vimrc:
+
+" Auto complete projects
+au filetype todo imap + +<C-X><C-U>
+" Auto complete contexts
+au filetype todo imap @ @<C-X><C-U>
+
+===============================================================================
+COMPLETION                                                      *todo-complete*
+
+The TodoComplete function is designed to complete projects (starting by '+')
+and context (starting by '@'). If you use it on a regulard word, it will do a
+normal buffer completion.
+If you try to complete a project, it will propose all projects in the file and
+for each of them, it will show their context in the preview window.
+TodoCompelte does the same thing for context except that it gives in the
+preview the list of projects existing in each existing contexts.