docs: note required value for clone-recursive in wrap

Fixes #13821 but perhaps a separate ticket should be opened for a
related bug, or maybe some extra docs are needed. Note in the ticket I
mentioned three things I had to do to get it working as expected after
the failures.

docs/markdown/Wrap-dependency-system-manual.md

@@ -135,7 +135,7 @@ case, the directory will be copied into `subprojects/` before applying patches.
 - `push-url` - alternative url to configure as a git push-url. Useful if
   the subproject will be developed and changes pushed upstream.
   *(since 0.37.0)*
-- `clone-recursive` - also clone submodules of the repository
+- `clone-recursive = true` - also clone submodules of the repository
   *(since 0.48.0)*
 
 ## wrap-file with Meson build patch