Add file input plugin and grok parser (#4332)

plugins/inputs/file/README.md

@@ -0,0 +1,25 @@
+# File Input Plugin
+
+The file plugin updates a list of files every interval and parses the contents
+using the selected [input data format](/docs/DATA_FORMATS_INPUT.md).
+
+Files will always be read in their entirety, if you wish to tail/follow a file
+use the [tail input plugin](/plugins/inputs/tail) instead.
+
+### Configuration:
+```toml
+[[inputs.file]]
+  ## Files to parse each interval.
+  ## These accept standard unix glob matching rules, but with the addition of
+  ## ** as a "super asterisk". ie:
+  ##   /var/log/**.log     -> recursively find all .log files in /var/log
+  ##   /var/log/*/*.log    -> find all .log files with a parent dir in /var/log
+  ##   /var/log/apache.log -> only tail the apache log file
+  files = ["/var/log/apache/access.log"]
+
+  ## Data format to consume.
+  ## Each data format has its own unique set of configuration options, read
+  ## more about them here:
+  ## https://github.com/influxdata/telegraf/blob/master/docs/DATA_FORMATS_INPUT.md
+  data_format = "influx"
+```