Add LVM example to Filebeat file / device ID docs

filebeat/docs/inputs/input-filestream-file-options.asciidoc

@@ -527,6 +527,9 @@ duplicated events in the output.
 
 *`native`*:: The default behaviour of {beatname_uc} is to differentiate
 between files using their inodes and device ids.
++
+In some cases these values can change during the lifetime of a file. 
+For example, when using the Linux link:https://en.wikipedia.org/wiki/Logical_Volume_Manager_%28Linux%29[LVM] (Logical Volume Manager), device numbers are allocated dynamically at module load (refer to link:https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/logical_volume_manager_administration/lv#persistent_numbers[Persistent Device Numbers] in the Red Hat Enterprise Linux documentation). To avoid the possibility of data duplication in this case, you can set `file_identity` to `path` rather than `native`.
 
 [source,yaml]
 ----

filebeat/docs/inputs/input-filestream.asciidoc

@@ -94,7 +94,7 @@ By default, {beatname_uc} identifies files based on their inodes and
 device IDs. However, on network shares and cloud providers these
 values might change during the lifetime of the file. If this happens
 {beatname_uc} thinks that file is new and resends the whole content
-of the file. To solve this problem you can configure `file_identity` option. Possible
+of the file. To solve this problem you can configure the `file_identity` option. Possible
 values besides the default `inode_deviceid` are `path`, `inode_marker` and `fingerprint`.
 
 WARNING: Changing `file_identity` methods between runs may result in