[docs] Dependencies are not clear on container

[alexrecuenco]

The dependencies are not clear on the container, the documentation states

• Container actions will have to specify the entrypoint, since the default entrypoint will be overridden to run the commands from the workflow.
• Container actions need to have the following binaries in their container image: sh, env, tail.

However, with the new implementation, it needs to have a GNU compatible stat a GNU compatible find, cp, exec, mkdir, and tar AFAIK. It would be nice to mention this in the documentation. Especially since it is a type of breaking change