Remove link to nabble in readme
Remove link to nabble in readme

Currently, no proper archive is available:
 * Nabble no longer archives Metafacture
 * Gmane is being relaunched and the archive of the Metafacture list is not (yet?) available
 * The archive at mail-archive.com is rather incomplete. It does not make much sense to link to it
cboehme/metafacture-core,culturegraph/metafacture-core,cboehme/metafacture-core,culturegraph/metafacture-core,metafacture/metafacture-core,culturegraph/metafacture-core,hbz/metafacture-core,metafacture/metafacture-core,hbz/metafacture-core,hbz/metafacture-core,metafacture/metafacture-core,cboehme/metafacture-core,cboehme/metafacture-core