Default value and docstring of org-attach-store-link-p

[Ihor Radchenko]

The default value of org-attach-store-link-p is nil for now.
Would it make more sense to set it to something else (say, 'attach)?
I believe that 'attach or t would be better as a default.

Thoughts?

Also, the docstring does not mention that there may be several different
non-nil values. It is only reflected in the :type field of defcustom.

Best,
Ihor