Description in repo not used if not using scan-path

[Jason at zx2c4.com (Jason A. Donenfeld)]

It looks like we get description from gitweb.description, inside the git config:

        else if (!strcmp(key, "gitweb.description"))
                config_fn(repo, "desc", value);

We alternatively get it from the description file:

        if (repo->desc == cgit_default_repo_desc || !repo->desc) {
                strbuf_addstr(path, "description");
                if (!stat(path->buf, &st))
                        readfile(path->buf, &repo->desc, &size);
                strbuf_setlen(path, pathlen);
        }

It may be smart to support both of these in that function. I'll see if
I can build in description scanning. I'm not completely convinced we
want it (after all, scan-path is _not_ defined in this case), but I'll
look into it.