installation: switch to YAML config files by default

Signed-off-by: Patrick Stephens <[email protected]>

Author: Patrick Stephens

installation/upgrade-notes.md

@@ -9,6 +9,15 @@ Note: release notes will be prepared in advance of a Git tag for a release so an
 The tag drives the overall binary release process so release binaries (containers/packages) will appear after a tag and its associated release note.
 This allows users to expect the new release binary to appear and allow/deny/update it as appropriate in their infrastructure.
 
+## Fluent Bit v4.0+
+
+The default configuration file has been switched to use YAML format and a different name (`.yaml` file suffix instead of `.conf`).
+
+This may require updating any custom deployments to either provide a YAML configuration or switch back to using legacy configuration in the arguments to the Fluent Bit binary.
+
+For Linux the Systemd unit will need overriding to specify `-c <legacy config file>`.
+Similarly for containers, Windows and macOS the default launch command is changed to point at the YAML config file by default.
+
 ## Fluent Bit v1.9.9
 
 The `td-agent-bit` package is no longer provided after this release.