Added a bit of documentation to README.markdown

README.markdown

@@ -3,3 +3,14 @@
     git clone git://github.com/freitass/todo.txt-vim.git
     cd todo.txt-vim
     cp -R * ~/.vim
+
+
+This plugin gives syntax highlighting to [todo.txt](http://todotxt.com/) files. It also defines a few
+mappings, to help with edition of these files:
+
+`<leader>-s` : Sort the file
+
+`<leader>-d` : Insert the current date
+
+`date<tab>` : (Insert mode) Insert the current date
+