Add a proper documentation about having both authentication and working download

on Sony PRS-TX. It could be better it will do for now. re #120

.htaccess

@@ -61,6 +61,12 @@ ExpiresByType text/javascript "access plus 1 year"
 ###########################################
 # Uncomment if you wish to protect access with a password
 ###########################################
+# If your covers and books are not available as soon as you protect it
+# You can try replacing the FilesMatch directive by this one
+# <FilesMatch "(index|feed)\.php">
+# If helps for Sony PRS-TX and Aldiko, beware fetch.php can be accessed
+# with authentication
+###########################################
 #<FilesMatch "\.php$">
 #AuthUserFile /path/to/file
 #AuthGroupFile /dev/null