out_loki: make it clear setting labels removes the keys from record

Related to the pull request fluent/fluent-bit#9766
The documentation doesn't make it clear, but the code seems to be
trying to work this way.

Also minor typo fix.

Signed-off-by: jantti <jantti@tri-ace.co.jp>

Author: ajantti

pipeline/outputs/loki.md

@@ -35,7 +35,7 @@ Be aware there is a separate Golang output plugin provided by [Grafana](https://
 
 ## Labels
 
-Loki store the record logs inside Streams, a stream is defined by a set of labels, at least one label is required.
+Loki stores the record logs inside Streams, a stream is defined by a set of labels, at least one label is required.
 
 Fluent Bit implements a flexible mechanism to set labels by using fixed key/value pairs of text but also allowing to set as labels certain keys that exists as part of the records that are being processed.
 Consider the following JSON record \(pretty printed for readability\):
@@ -88,6 +88,8 @@ When processing that new configuration, the internal labels will be:
 job="fluentbit", mystream="stdout"
 ```
 
+Extracting keys to labels through `labels`, `label_keys` or `label_map_path` will remove those keys from the record.
+
 ### Using the `label_keys` property
 
 The additional configuration property called `label_keys` allow to specify multiple record keys that needs to be placed as part of the outgoing Stream Labels, yes, this is a similar feature than the one explained above in the `labels` property.