[chore][receiver/filelog] docs: fix docs on setting header to `fals…

…e` (#35864)

Setting `heaader` to `false` results in error when starting the
collector. The value of `header` must either be a map or `null`.

receiver/filelogreceiver/README.md

@@ -45,7 +45,7 @@ Tails and parses logs from files.
 | `resource` | {} | A map of `key: value` pairs to add to the entry's resource. |
 | `operators` | [] | An array of [operators](../../pkg/stanza/docs/operators/README.md#what-operators-are-available). See below for more details. |
 | `storage` | none | The ID of a storage extension to be used to store file offsets. File offsets allow the receiver to pick up where it left off in the case of a collector restart. If no storage extension is used, the receiver will manage offsets in memory only. |
-| `header` | nil | Specifies options for parsing header metadata. Requires that the `filelog.allowHeaderMetadataParsing` feature gate is enabled. See below for details. Must be `false` when `start_at` is set to `end`. |
+| `header` | nil | Specifies options for parsing header metadata. Requires that the `filelog.allowHeaderMetadataParsing` feature gate is enabled. See below for details. Must not be set when `start_at` is set to `end`. |
 | `header.pattern` | required for header metadata parsing | A regex that matches every header line. |
 | `header.metadata_operators` | required for header metadata parsing | A list of operators used to parse metadata from the header. |
 | `retry_on_failure.enabled` | `false` | If `true`, the receiver will pause reading a file and attempt to resend the current batch of logs if it encounters an error from downstream components. |