send-email: update documentation of required Perl modules

Improve and complete the list of required email related Perl modules,
clarifying which are core Perl modules and remove Net::SMTP::SSL.

git-send-email uses the TLS support in the Net::SMTP core module from
recent versions of Perl. Documenting the minimum version is complex
because of separate numbering for Perl (5.21.5~169), Net:SMTP (2.34)
and libnet (3.01). Version numbers from commit:
bfbfc9a953 ("send-email: Net::SMTP::starttls was introduced in v2.34",
2017-05-31).

Users of older Perl versions without Net::SMTP::SSL installed will get a
clear error message.

Signed-off-by: Chris Mayo <aklhfex@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-send-email.txt

@@ -500,8 +500,12 @@ app-specific or your regular password as appropriate.  If you have credential
 helper configured (see linkgit:git-credential[1]), the password will be saved in
 the credential store so you won't have to type it the next time.
 
-Note: the following perl modules are required
-      Net::SMTP::SSL, MIME::Base64 and Authen::SASL
+Note: the following core Perl modules that may be installed with your
+distribution of Perl are required:
+MIME::Base64, MIME::QuotedPrint, Net::Domain and Net::SMTP.
+These additional Perl modules are also required:
+Authen::SASL and Mail::Address.
+
 
 SEE ALSO
 --------