readme.md: use docs.cilium.io instead of cilium.readthedocs.io
readme.md: use docs.cilium.io instead of cilium.readthedocs.io

Signed-off-by: Tobias Klauser <9249c549618448e4c699e8032ba6c7f0d7fd4b7f@distanz.ch>

cilium/ebpf,cilium/ebpf