Update readme

Begin logging
Account for fb2 books without covers

lector/threaded.py

@@ -16,6 +16,7 @@
 
 import os
 import re
+import logging
 import pathlib
 
 from multiprocessing.dummy import Pool
@@ -24,6 +25,8 @@ from PyQt5 import QtCore, QtGui
 from lector import sorter
 from lector import database
 
+logger = logging.getLogger(__name__)
+
 
 class BackGroundTabUpdate(QtCore.QThread):
     def __init__(self, database_path, all_metadata, parent=None):