Bug#1077313: release-notes: Add -f parameter to script in section 4.4.1

[Ariel <asdebian@dsgml.com>]

Package: release-notes
Severity: normal

The advice to record the upgrade session using the script command in section 4.4.1 should include the -f flag.

There are two reasons for this:

1: If the system crashes the session log will be as current as possible.
2: The document recommends switching to VT2 to view the file, however without -f you won't see any output in the file, or at least not current output.

-- System Information:
Debian Release: 9.13
  APT prefers oldoldstable
  APT policy: (990, 'oldoldstable')
Architecture: i386 (x86_64)
Foreign Architectures: amd64

Kernel: Linux 4.9.320 (SMP w/8 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE= (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)