Add documentation for daily Japanese

docs/japanese.rst

@@ -5,11 +5,31 @@ Daily Japanese Lesson
 How It Works
 ------------
 
+One of the functionality of Maid-chan's scheduler worker is daily Japanese lesson. Currently, daily Japanese lesson sends a random kanji based on user's level selection (N1 - N4) and a random vocabulary (same for all levels) every 13:00 UTC+9.
+
+The raw data is parsed from `Gakuran`_ and currently stored under `data/` directory.
+
+.. autofunction:: maidchan.japanese.get_kanji
+
+Since the source data follows old format of JLPT test, there are only 4 levels in it: N1 to N4. `get_kanji` reads a certain line (`current_pos`) based on level selection from the file and returns it to the caller.
+
+.. autofunction:: maidchan.japanese.get_vocabulary
+
+The original data does not distinguish vocabulary based on JLPT levels. Therefore, it only accepts a certain line (`current_pos`), reads it from the file, and returns it to the caller.
+
+.. autofunction:: maidchan.japanese.get_japanese_message
+
+Finally, scheduler calls `get_japanese_message` to construct a daily lesson message.
+
 How to Run
 ----------
 
-Japanese Kanji
---------------
+1. You can start running scheduler by executing:
+
+.. code-block:: bash
+
+   $ maidchan_scheduler
+
+2. You can subscribe & unsubscribe to Maid-chan's daily Japanese lesson via `subscribe japanese` and `unsubscribe japanese` command in the Messenger.
 
-Japanese Vocabulary
--------------------
+.. _Gakuran: http://gakuran.com/japanese-csv-database/