added vim doc and instructions to rebuild help tags

README.markdown

@@ -16,3 +16,5 @@ mappings, to help with edition of these files:
 
 `date<tab>` : (Insert mode) Insert the current date
 
+If you want the help installed run ":helptags ~/.vim/doc" inside vim after having copied the files.
+Then you will be able to get the commands help with: :h todo.txt

doc/todo.txt

@@ -0,0 +1,14 @@
+*todo.txt*
+
+==============================================================================
+COMMANDS                                                       *todo-commands*
+
+`<Leader>-s` : Sort the file
+
+`<Leader>-d` : Insert the current date
+
+`<Leader>-D` : Insert the current date with leading `x` (completed)
+
+`date<tab>` : (Insert mode) Insert the current date
+
+<Leader> is \ by default, so <Leader>-s means you type \s