Update docs for --pluginpath

Fixes #3630

docs/asciidoc/static/command-line-flags.asciidoc

@@ -19,19 +19,37 @@ display this information.)
  is specified, 'stdout { codec => rubydebug }}' is default.
 
 -w, --filterworkers COUNT
- Run COUNT filter workers (default: 1)
+ Sets the number of filter workers to run (default: 1)
 
 --watchdog-timeout TIMEOUT
- Set watchdog timeout value in seconds. Default is 10.
+ Set watchdog timeout value in seconds. Default is 10. This timeout is used to detect
+ stuck filters; stuck filters usually symptoms of bugs. When a filter takes longer than 
+ TIMEOUT seconds, it will cause Logstash to abort.
 
 -l, --log FILE
  Log to a given path. Default is to log to stdout
 
 --verbose
- Increase verbosity to the first level, less verbose.
+ Increase verbosity to the first level (info), less verbose.
 
 --debug
- Increase verbosity to the last level, more verbose.
+ Increase verbosity to the last level (trace), more verbose.
+
+-V, --version
+  Display the version of Logstash.
+
+-p, --pluginpath
+  A path of where to find plugins. This flag can be given multiple times to include
+  multiple paths. Plugins are expected to be in a specific directory hierarchy:
+  'PATH/logstash/TYPE/NAME.rb' where TYPE is 'inputs' 'filters', 'outputs' or 'codecs'
+  and NAME is the name of the plugin.
+
+-t, --configtest
+  Checks configuration and then exit. Note that grok patterns are not checked for 
+  correctness with this flag
+
+-h, --help
+  Print help  
 
 -v
  *DEPRECATED: see --verbose/debug* Increase verbosity. There are multiple levels