the readme is confusing

[chunhualiao]

2. Build docker

• There are another README.md under infant/computer: it mentions two versions of ubuntu 22.04 vs. 18.04. And 22.04 will have problem. But the instructions so far all mention 22.04.
• run_docker.sh picks 18.04 as default

suggestion:

• merge all instructions to top level README.md
• clarify exactly which version of ubuntu should be used.

[bin123apple]

Just updated the package updating parts: aab3a0e, I will updated a pre-built docker soon.

[bin123apple]

Just update the readme and the docker again.