Add ppid to ps examples

[pingiun]

Note that this is unreleased. This PR should be blocked until nushell/nushell#8750 has landed in a release

[hustcer]

Thanks for the PR, commands/docs/ps.md need not be modified, as all docs in commands/docs folder were created by a script, they will be updated after next nushell release. You can update the examples fn in crates/nu-command/src/system/ps.rs to add more examples

[fdncred]

I think the examples are probably fine to leave here but the commands/docs/ps.md will get overwritten as hustcer has said.

[hustcer]

Thanks, we will merge it after nu v0.79 been released