Update usage information

README.md

@@ -22,26 +22,15 @@ re-writing chat history.
 
 ## Usage
 
-To list available boards:
-
-```
-bulb
 ```
+bulb: bulletin board
 
-To post a message:
+Usage: bulb [-hlpu] [-b <board>] [-n <number>]
 
+-h: print this help text
+-b <board>: specify a board other than general
+-l: list available boards and exit
+-n <number>: display N most recent messages
+-p: post a message (from stdin)
+-u: operate undercover (anonymously)
 ```
-bulb post
-bulb post -b <board-name>
-```
-
-To read recent messages:
-
-```
-bulb read
-bulb read -b <board-name>
-bulb read -n <message-count>
-```
-
-Note that when not specified, the board name defaults to `general`. For this
-reason, it is recommended to ensure that a board with this name exists.