Update README to reflect seelog removal.

Author: jrick

README.md

@@ -5,15 +5,8 @@ btclog
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-Package btclog implements a subsystem aware logger backed by seelog.
-
-Seelog allows you to specify different levels per backend such as console and
-file, but it doesn't support levels per subsystem well.  You can create multiple
-loggers, but when those are backed by a file, they have to go to different
-files.  That is where this package comes in.  It provides a SubsystemLogger
-which accepts the backend seelog logger to do the real work.  Each instance of a
-SubsystemLogger then allows you specify (and retrieve) an individual level per
-subsystem.  All messages are then passed along to the backend seelog logger.
+Package btclog defines a logger interface and provides a default implementation
+of a subsystem-aware leveled logger implementing the same interface.
 
 ## Installation