Update readme

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Account for fb2 books without covers

lector/readers/read_epub.py

@@ -15,11 +15,14 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 import os
+import logging
 import zipfile
 from urllib.parse import unquote
 
 from bs4 import BeautifulSoup
 
+logger = logging.getLogger(__name__)
+
 
 class EPUB:
     def __init__(self, filename):
@@ -189,7 +192,7 @@ class EPUB:
             if biggest_image:
                 self.book['cover'] = self.read_from_zip(biggest_image)
             else:
-                print('No cover found for: ' + self.filename)
+                logger.error('No cover found for: ' + self.filename)
 
         # Parse spine and arrange chapter paths acquired from the opf
         # according to the order IN THE SPINE