adds "since"-note for the new keyword to the documentation

docs/markdown/Qt5-module.md

@@ -8,7 +8,7 @@ tools and steps required for Qt. The module has one method.
 This method takes the following keyword arguments:
  - `moc_headers`, `moc_sources`, `ui_files`, `qresources`, which define the files that require preprocessing with `moc`, `uic` and `rcc`
  - `include_directories`, the directories to add to header search path for `moc` (optional)
- - `moc_extra_arguments`, any additional arguments to `moc` (optional).
+ - `moc_extra_arguments`, any additional arguments to `moc` (optional). Available since v0.44.0.
 
 It returns an opaque object that should be passed to a main build target.