bug#25093: Configure file for system-wide substitutes

[Hartmut Goebel]

Hi,

when publishing packages in the local network, one wants to use this
substitute without passing --substitute-urls on every relevant run on guix.

I suggest implementing a config-file for storing the substitute-urls,
much like the sources.list on Debian systems.

In the long run we'll need this for enterprise setup anyway :-)
Enterprises tend to fetch software from their internal  repositories only .

-- 
Regards
Hartmut Goebel

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