lsof: add -u, -c example and note about privileges

pages/common/lsof.md

@@ -1,6 +1,7 @@
 # lsof
 
 > Lists open files and the corresponding processes
+> Note: In most case, you need root privilege (or sudo) because you want to list files opened by other than you.
 
 - find the processes that have a given file open
 
@@ -13,3 +14,11 @@
 - only output the process PID (e.g. to pipe into kill)
 
 `lsof -t {{/path/to/file}} | xargs kill -9`
+
+- list files opened by user
+
+`lsof -u {{username}}`
+
+- list files opened by command (or process) name (e.x nginx)
+
+`lsof -c {{process_or_command_name}}`