Add README.

README.md

+Topydo
+======
+
+Topydo is a todo list application using the [todo.txt format][1]. It is heavily
+inspired by the [todo.txt CLI][1] by Gina Trapani. This tool is actually a
+merge between the todo.txt CLI and a [number of extensions][3] that I wrote
+on top of the CLI, hereafter refered to as todo.txt-tools. These extensions
+are:
+
+* Set **due** and **start dates**;
+* Custom sorting;
+* Dealing with tags;
+* Maintain **dependencies** between todo items;
+* Allow todos to **recur**;
+* Some conveniences when adding new items (e.g. adding creation date and use
+  **relative dates**);
+
+Current status
+--------------
+
+The feature set is not yet on-par with todo.txt CLI + todo.txt-tools combined.
+Missing features are easy sorting, tag management and postponing todos.
+
+Subcommands implemented:
+
+* add
+* append
+* del
+* dep [x]
+* depri
+* do
+* ls
+* lscon
+* lsprj
+* pri
+
+Subcommands marked as [x] don't exist in the todo.txt CLI, but were added by
+todo.txt-tools.
+
+Motivation
+----------
+
+The motivation to rewrite the CLI from scratch was for multiple reasons.
+
+First, in the long term I'd like to write the perfect todo client. The perfect
+todo client is free, open source, flexible and available wherever I am.
+todo.txt is the perfect format, since it's simple and plain text and not bound
+to a particular tool.
+
+Second, the current (CLI) interface is handy, but has its limits when dealing
+with large swaths of todo items. The CLI and a GUI should complement each
+other.
+
+Third, the original todo.txt CLI is a huge Bash script. In my opinion it's the
+wrong language to write a serious application with it. It may behave
+differently on other operating systems (or sometimes it's plain broken). The
+todo.txt-tools that extend the CLI were (quickly) written in Perl. It doesn't
+have a proper test suite and it sometimes doesn't play very well when a user
+inputs something funny.
+
+In order to achieve the long term vision of a perfect todo list, I need a solid
+foundation in a solid language. Hence the rewrite in Python, sprinkeled with
+unit tests.
+
+References
+----------
+
+[1] https://github.com/ginatrapani/todo.txt-cli/wiki/The-Todo.txt-Format
+[2] https://github.com/ginatrapani/todo.txt-cli
+[3] https://github.com/bram85/todo.txt-tools