Explain what it means that Wireshark can now open PCAP files (as MIME files).

Explain what it means that Wireshark can now open PCAP files (as MIME files).

The title "New File Format Support" containing a list that included PCAP and
PCAPNG caught my eye: Wireshark has supported those for years.  (Attempt to)
explain what it means.

Change-Id: I472fabcca00befee9032cd7ef11bf30257b8ff8e
Reviewed-on: https://code.wireshark.org/review/11076
Reviewed-by: Anders Broman <a.broman58@gmail.com>
(cherry picked from commit 1a434143693a7f9ce103dfcf53e60c63415c81e8)
Reviewed-on: https://code.wireshark.org/review/11147
Reviewed-by: Jeff Morriss <jeff.morriss.ws@gmail.com>