Add link to vjeantet/grok to grok parser docs

plugins/parsers/grok/README.md

@@ -59,11 +59,15 @@ To match a comma decimal point you can use a period. For example `%{TIMESTAMP:t
 To match a comma decimal point you can use a period in the pattern string.
 See https://golang.org/pkg/time/#Parse for more details.
 
-Telegraf has many of its own [built-in patterns](/plugins/parsers/grok/influx_patterns.go),
-as well as support for most of
-[logstash's builtin patterns](https:/logstash-plugins/logstash-patterns-core/blob/master/patterns/grok-patterns).
-_Golang regular expressions do not support lookahead or lookbehind.
-logstash patterns that depend on these are not supported._
+Telegraf has many of its own [built-in patterns][] as well as support for most
+of the Logstash builtin patterns using [these Go compatible patterns][grok-patterns].
+
+**Note** Golang regular expressions do not support lookahead or lookbehind.
+Logstash patterns that use these features may not supported, or may use a Go
+friendly pattern that does is not always completely compatible with Logstash.
+
+[built-in patterns]: /plugins/parsers/grok/influx_patterns.go
+[grok-patterns]: https:/vjeantet/grok/blob/master/patterns/grok-patterns
 
 If you need help building patterns to match your logs,
 you will find the https://grokdebug.herokuapp.com application quite useful!

plugins/parsers/grok/influx_patterns.go

@@ -1,45 +1,6 @@
 package grok
 
 const DEFAULT_PATTERNS = `
-# Captures are a slightly modified version of logstash "grok" patterns, with
-# the format %{<capture syntax>[:<semantic name>][:<modifier>]}
-# By default all named captures are converted into string fields.
-# If a pattern does not have a semantic name it will not be captured.
-# Modifiers can be used to convert captures to other types or tags.
-# Timestamp modifiers can be used to convert captures to the timestamp of the
-# parsed metric.
-
-# View logstash grok pattern docs here:
-# https://www.elastic.co/guide/en/logstash/current/plugins-filters-grok.html
-# All default logstash patterns are supported, these can be viewed here:
-# https:/logstash-plugins/logstash-patterns-core/blob/master/patterns/grok-patterns
-
-# Available modifiers:
-# string (default if nothing is specified)
-# int
-# float
-# duration (ie, 5.23ms gets converted to int nanoseconds)
-# tag (converts the field into a tag)
-# drop (drops the field completely)
-# Timestamp modifiers:
-# ts-ansic ("Mon Jan _2 15:04:05 2006")
-# ts-unix ("Mon Jan _2 15:04:05 MST 2006")
-# ts-ruby ("Mon Jan 02 15:04:05 -0700 2006")
-# ts-rfc822 ("02 Jan 06 15:04 MST")
-# ts-rfc822z ("02 Jan 06 15:04 -0700")
-# ts-rfc850 ("Monday, 02-Jan-06 15:04:05 MST")
-# ts-rfc1123 ("Mon, 02 Jan 2006 15:04:05 MST")
-# ts-rfc1123z ("Mon, 02 Jan 2006 15:04:05 -0700")
-# ts-rfc3339 ("2006-01-02T15:04:05Z07:00")
-# ts-rfc3339nano ("2006-01-02T15:04:05.999999999Z07:00")
-# ts-httpd ("02/Jan/2006:15:04:05 -0700")
-# ts-epoch (seconds since unix epoch)
-# ts-epochnano (nanoseconds since unix epoch)
-# ts-"CUSTOM"
-# CUSTOM time layouts must be within quotes and be the representation of the
-# "reference time", which is Mon Jan 2 15:04:05 -0700 MST 2006
-# See https://golang.org/pkg/time/#Parse for more details.
-
 # Example log file pattern, example log looks like this:
 # [04/Jun/2016:12:41:45 +0100] 1.25 200 192.168.1.1 5.432µs
 # Breakdown of the DURATION pattern below: