Split parser/serializer docs (#4690)

plugins/parsers/influx/README.md

@@ -0,0 +1,20 @@
+# InfluxDB Line Protocol
+
+There are no additional configuration options for InfluxDB [line protocol][]. The
+metrics are parsed directly into Telegraf metrics.
+
+[line protocol]: https://docs.influxdata.com/influxdb/latest/write_protocols/line/
+
+### Configuration
+
+```toml
+[[inputs.file]]
+  files = ["example"]
+
+  ## 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"
+```
+