man update: document -pp and make the defult print format more clear

Author: ldegio

userspace/sysdig/man/sysdig.md

@@ -22,7 +22,7 @@ sysdig includes a powerul filtering language, has customizable output, and can b
 
 By default, sysdig prints the information for each captured event on a single line, with the following format:
 
-```<evt.num> <evt.time> <evt.cpu> <proc.name> <thread.tid> <evt.dir> <evt.type> <evt.args>```
+```*%evt.num %evt.time %evt.cpu %proc.name (%thread.tid) %evt.dir %evt.type %evt.info```
 
 where:
 * evt.num is the incremental event number
@@ -38,7 +38,7 @@ The output format can be customized with the -p switch, using any of the fields
 
 Using -pc or -pcontainer, the default format will be changed to a container-friendly one:
 
-```%evt.num %evt.time %evt.cpu %container.name (%container.id) %proc.name (%thread.tid:%thread.vtid) %evt.dir %evt.type %evt.info```
+```*%evt.num %evt.time %evt.cpu %container.name (%container.id) %proc.name (%thread.tid:%thread.vtid) %evt.dir %evt.type %evt.info```
 
 **Trace Files**  
 
@@ -151,7 +151,7 @@ OPTIONS
   Print progress on stderr while processing trace files.
 
 **-p** _outputformat_, **--print**=_outputformat_  
-  Specify the format to be used when printing the events. With -pc or -pcontainer will use a container-friendly format. See the examples section below for more info.
+  Specify the format to be used when printing the events. With -pc or -pcontainer will use a container-friendly format. See the examples section below for more info. Specifying **-pp** on the command line will cause sysdig to print the default command line format and exit.
 
 **-q**, **--quiet**  
   Don't print events on the screen. Useful when dumping to disk.