Add info about the base image used and the github repo of
elasticsearch-docker.
Clarify that setting `memlock=-1:-1` is only a requirement when
`bootstrap_memory_lock=true` and the alternatives we document
elsewhere in docs for disabling swap are valid for Docker as well.
Additionally, with latest versions of docker-ce shipping with
unlimited (or high enough) defaults for `nofile` and `nproc`, clarify
that explicitly setting those per ES container is not required, unless
they are not defined in the Docker daemon.
Finally simplify production `docker-compose.yml` example by removing
unneeded options.
Relates #24389
79857357bf