german@Debian:~$  sed -e '1,/#An extra directory/d' -e '/For example/,20d'  foo.lst
8
9
10
11
12
13
14
german@Debian:~$ cat foo.lst
1
2
3
4
5
6
#An extra directory
8
9
10
11
12
13
14
For example
16
17
18
19
20
german@Debian:~$