doc: fix missing kwarg in qt5 module

compile_moc accepts "dependencies" for the same reason preprocess does,
but the original documentation never copied this over from the
preprocess docs.

See: https://github.com/mesonbuild/meson/issues/9683#issuecomment-986825041

docs/markdown/_include_qt_base.md

@@ -46,6 +46,7 @@ It takes no positional arguments, and the following keyword arguments:
   - `extra_args` string[]: Extra arguments to pass directly to `qt-moc`
   - `method` string: The method to use to detect qt, see `dependency()` for more
     information.
+  - `dependencies`: dependency objects whose include directories are used by moc.
   - `include_directories` (string | IncludeDirectory)[]: A list of `include_directory()`
     objects used when transpiling the .moc files