Merge branch 'jt/clone-recursesub-ref-advise'

The interaction between "git clone --recurse-submodules" and
alternate object store was ill-designed.  The documentation and
code have been taught to make more clear recommendations when the
users see failures.

* jt/clone-recursesub-ref-advise:
  submodule--helper: advise on fatal alternate error
  Doc: explain submodule.alternateErrorStrategy

diff --cc builtin/submodule--helper.c
index a4f9f8d,12d546d..c72931e
--- 1/builtin/submodule--helper.c
--- 2/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@@ -19,7 -19,7 +19,8 @@@
  #include "diffcore.h"
  #include "diff.h"
  #include "object-store.h"
 +#include "dir.h"
+ #include "advice.h"
  
  #define OPT_QUIET (1 << 0)
  #define OPT_CACHED (1 << 1)