in_prometheus_remite_write: Add a description of uri parameter (#1382)

Signed-off-by: Hiroshi Hatake <[email protected]>

Author: cosmo0920

pipeline/inputs/prometheus-remote-write.md

@@ -16,7 +16,7 @@ This input plugin allows you to ingest a payload in the Prometheus remote-write
 | buffer\_chunk\_size | This sets the chunk size for incoming incoming JSON messages. These chunks are then stored/managed in the space available by buffer_max_size.  | 512K    |
 |successful\_response\_code | It allows to set successful response code. `200`, `201` and `204` are supported.| 201 |
 | tag\_from\_uri      | If true, tag will be created from uri, e.g. api\_prom\_push from /api/prom/push, and any tag specified in the config will be ignored. If false then a tag must be provided in the config for this input. | true    |
-
+| uri               | Specify an optional HTTP URI for the target web server listening for prometheus remote write payloads, e.g: /api/prom/push                       | |
 
 
 A sample config file to get started will look something like the following: