docs: build_always_stale was added in 0.47 [skip ci]

docs/markdown/Reference-manual.md

@@ -264,7 +264,7 @@ following.
 - `build_always` (deprecated) if `true` this target is always considered out of
   date and is rebuilt every time.  Equivalent to setting both
   `build_always_stale` and `build_by_default` to true.
-- `build_always_stale` if `true` the target is always considered out of date.
+- `build_always_stale` *(added 0.47)* if `true` the target is always considered out of date.
   Useful for things such as build timestamps or revision control tags.
   The associated command is run even if the outputs are up to date.
 - `capture`, there are some compilers that can't be told to write