system-config: back up nas_audiobooks mount fix and missing unit files

Adds the 4 permanent .mount units (family/books/owncloud/audiobooks) and
audiobookshelf-mount-ready.service to the repo backup, which weren't
tracked here yet, and updates the README to document the autofs->permanent
mount fix applied to nas_audiobooks today so a host rebuild doesn't
recreate the broken automount version.

system-config/nfs-self-heal/mnt-nas_audiobooks.mount

@@ -0,0 +1,13 @@
+[Unit]
+Description=Mount unRAID audiobooks NFS share
+After=network-online.target
+Wants=network-online.target
+
+[Mount]
+What=192.168.1.192:/mnt/user/media/audiobooks
+Where=/mnt/nas_audiobooks
+Type=nfs
+Options=nfsvers=3,hard,rw,noatime
+
+[Install]
+WantedBy=multi-user.target