added defaultNetstreamDriverCertFile to global()
added defaultNetstreamDriverCertFile to global()

This is the doc counterpart of: https://github.com/rsyslog/rsyslog/pull/45

Plus a few more words about those TLS options.
luozhihui/rsyslog-doc,ribeiropaulor/rsyslog-doc,sematext/rsyslog-doc,Whissi/rsyslog-doc,qha/rsyslog-doc,rcuza/rsyslog-doc,qha/rsyslog-doc,teifler/rsyslog-doc,janmejay/rsyslog-doc,taotetek/rsyslog-doc,volter/rsyslog-doc,jite/rsyslog-doc,janmejay/rsyslog-doc,taotetek/rsyslog-doc,qha/rsyslog-doc,luozhihui/rsyslog-doc,teifler/rsyslog-doc,sematext/rsyslog-doc,rcuza/rsyslog-doc,luozhihui/rsyslog-doc,qha/rsyslog-doc,volter/rsyslog-doc,sematext/rsyslog-doc,jite/rsyslog-doc,volter/rsyslog-doc,mbiebl/rsyslog-doc,teifler/rsyslog-doc,luozhihui/rsyslog-doc,sematext/rsyslog-doc,janmejay/rsyslog-doc,ribeiropaulor/rsyslog-doc,volter/rsyslog-doc,mbiebl/rsyslog-doc,Whissi/rsyslog-doc,janmejay/rsyslog-doc,ribeiropaulor/rsyslog-doc,taotetek/rsyslog-doc,teifler/rsyslog-doc,Whissi/rsyslog-doc,mbiebl/rsyslog-doc,rcuza/rsyslog-doc,jite/rsyslog-doc,taotetek/rsyslog-doc,rcuza/rsyslog-doc,Whissi/rsyslog-doc,jite/rsyslog-doc,ribeiropaulor/rsyslog-doc