git-imap-send.txt: do verify SSL certificate for gmail.com

git-imap-send.txt: do verify SSL certificate for gmail.com

As a public service, it is unlikely that the Gmail server is configured
to throw a certificate that does not verify at the user.

Remove the `sslVerify=false` config from the Gmail example.

Also, comment it in the `example.com` example, and add a note to the
user explaining that they might want to uncomment it if they are having
trouble connecting. While at it, use an Asciidoc 'Note' section in the
Gmail example also.

Based-on-patch-by: Barbu Paul - Gheorghe <barbu.paul.gheorghe@gmail.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>