FAQ October 2019 update

[Robert J. Hansen]

The last time I gave the FAQ a thorough read-and-review was in October
2017, so it was time for a review.  I fought off the urge to rewrite the
thing entirely -- I really don't like how it flows, but I view my job as
maintainer is more about making minor incremental changes than total
rewrites whenever the whim seizes me.

Anyway, the major changes:

* Every reference to the SKS keyserver network now points to
keys.openpgp.org.  Reason: the SKS attacks a few months ago.

* All references to 2048-bit crypto are updated to refer to 3072-bit
crypto.  Reason: GnuPG now defaults to 3072-bit RSA.

* PGPNET's email address has changed.


... Those were the high-priority changes that needed to be made.  If
anyone has other suggestions, speak up: I'm listening.  :)

(Note: I just committed the FAQ changes.  It may take a couple of days
for the documentation on the website to be regenerated.)