An alist of archives from which to fetch.
The default value points to the GNU Emacs package repository.
Each element has the form (ID . LOCATION).
ID is an archive name, as a string.
LOCATION specifies the base location for the archive.
If it starts with "http:", it is treated as a HTTP URL;
otherwise it should be an absolute directory name.
(Other types of URL are currently not supported.)
Only add locations that you trust, since fetching and installing
a package can run arbitrary code.