emacstips: invoking the external html viewer

Rewrite because the information was mostly obsolete *and* we couldn't
reach the author of existing text for license change:

commit 703ae92a5c0acdbea5384b36b78ea341e0b07da1
Author: Konrad Scorciapino <konrad@scorciapino.com>
Date:   Wed Mar 23 16:20:16 2011 -0300

    html rendering

Please don't resurrect that text without proper license.
Revert "Added another way to set the from address automatically when sending mail through msmtp."

This reverts commit f1bc6af50df4383abc038fd22d26356eb18075bc, because
the author was not reachable for a license change. Please do not bring
back the content without proper licensing.
wikiwriteaccess: require valid user.name and user.email