Clarify the INSTALL instructions

Ensure users understand that they need to have appropriate permissions
to write to the install location.

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/9268)

(cherry picked from commit 7c03bb9fff02b7f08d4654f51f8667584a92cf72)