Add more Job examples

Start by reading the README Job example and the Job-related tests, especially the cases covering callbacks, environments, writers, and sending arguments to a running command. Verify each requested behavior from those tests before expanding the documentation. Done means a minimal example and clear examples or explanations for environment inheritance, PATH handling, piping, sequencing, cleanup, and job reuse.

Hello.
Thank you for the thing that is closer to a stdlib for neovim plugin development in Lua.
The thing I find more interesting in this library is the job interface. There is no easy way to run terminal commands from neovim and job is a fantastic thing to have.
However, this is also one of the methods with less docs, so it is hard to understand what it can and cannot do. For example, I was not aware that you don't need to nest callbacks to get the result of the job, like the example shows in the on_exit callback, you can just get the results directly from the job return.
All the knowledge I have about it comes from reading the tests, which are a good kind of documentation, but it is kind of hidden and not all are fully readable.

The things I would love to have docs about are:

• Mention that not providing an environment, the job will inherit the current environment
• Mention that if you define an environment, binary executions will fail if you don't provide a proper PATH in that environment. Also an example of how to pass the current path will be interesting
• Document how to pipe commands. I think this is using the writer interface, but I am not sure
• Can I conditionally execute a job based on the results I get from the previous one? How can I ensure they are run in the right order? Is just calling one after the other enough?
• Show a very minimal example. The current example in the readme has a lot of fields, and it seems that all you need is the cmd property, which makes Job much more appealing and accessible.
• Do commands automatically finish? Or do I have to do some cleanup?
• Can I re-use a job? In the tests I saw there is the possibility to send arguments to a running command, but I am not sure how this works. Will it spawn a new command each time? Will it reuse the existing execution hence requiring a long-lived process?

Again, thank you very much