Document temporary character of references in repolist.rst

Document temporary character of references in repolist.rst

According to the comment in repolist.rst references there are only
temporary and should be removed when the project is referenced from
more appropriate place. Unfortunately developer may never notice this
comment as writting to this file in documentation is done by echo
command. To improve this situation let's add an explicit mention about
this temporary character of repolist.rst to the documentation.

Issue-ID: DOC-501
Signed-off-by: Krzysztof Opasiak <k.opasiak@samsung.com>
Change-Id: I8d8b5fe03d29b5141d57e1d06220bd6382a52861
(cherry picked from commit 6688fd00ba150d6bd5c4e2f6cb91dd0c88fbf371)