updates for TODO and README

* library support for setns() system call was added to glibc
version 2.14 (setns() call is use in src/machine/machinectl.c
and src/libsystemd-bus-container.c)

* utf8 validation call are already exported (via sd-utf8.c file) -
commit - 369c583b3fb3d672ef469d53141e274ec9d2e8a7
TODO: remove dbus requirement