Add basic postfix mail config in use on foghlaim.com

At some point it's best if this is transferred to a repository that manages the server, but for now it will do as part of this repository.

Just a basic config at the moment to get email sending from @foghlaim.com. Hopefully I can tweak this out and make it smoother all around, possibly for multiple domains.
Specify a mail hostname and a domain name rather than just a hostname
Clarify the use of the myorigin directive
Clarify some of the rules around receiving email at this domain, even if I'm not entirely familiar with it yet
Get explicit about who we trust to send mail through SMTP on this machine
Remove a duplicate, commented out myorigin directive
Additional explicit relay information
Add unclear clarification about alias_maps and alias_database
Clarify the default recipient_delimiter used by Postfix
Reorganize some stuff in main.cnf as we're going through the distribution example
Clarify the smtpd_banner directive, drop (Ubuntu) from text
Now that we've used the more complete version, drop the comment telling us to
Comment out some of the misc configuration directives in main.cnf
Additional commenting of the TLS related directives in main.cnf
Add note about DKIM. Will expand when tackling that portion of the config documentation.