luci-static/index_user.html: add new file, to work around broken "luc…

…i-mod-freifunk"

the content of the file will be displayed on the index-page of the router. 
The provided link gives a hint, how to read the LuCI-admin interface, as it's currently boken (see freifunk-berlin#831)

embedded-files/www/luci-static/index_user.html

@@ -0,0 +1 @@
+As the package "luci-mod-freifunk" / "luci-mod-freifunk" is broken, you can <a href='/cgi-bin/luci/admin/status/overview'>reach the admin interface via this link</a>.