server: add TLS and default to 127.0.0.1:4001 for etcd

When ETCD_MACHINES is not set, default to http://127.0.0.1:4001.
Also add ETCD_TLSKEY and ETCD_TLSPEM argument to setup an TLS
conn. with etcd. (not tested yet).
Add docs as todo
Update README
server: remove WriteTimeout config

Not used, so no sense in setting this.
Update the README