More example documentation for deploying Serverless

**Is your feature request related to a problem? Please describe.**

Currently, the [executor for the `setup` command assumes a Python + Node environment setup](https://github.com/CircleCI-Public/serverless-framework-orb/blob/master/src/executors/default.yml#L4).
> this is totally reasonable since we want to install aws-cli and serverless CLI.

If we are using the same executor within a job to also run steps to `command: serverless deploy`, this would of course, only work in the examples of a Python Lambda, and possibly Node (if using the defaulted image).

This would not seem to work for other languages, like Ruby for example.
> since packaging for Ruby dependencies would hit a wall in the same `cimg/python:xxx` executor.

**Describe the solution you'd like**

Initially, I was thinking if allowing more flexibility for the orb user to choose their executor / runtime in the `setup` command would be better since I can, for example, choose to use the `lambci/lambci:build-ruby2.5` to `serverless deploy` (in my case, I needed to deploy to AWS and so LambCI's docker images are useful for `serverless package`).

However, I think it's not the issue of the `setup` command, but more about adding more verbose examples of how to deploy for serverless functions of different languages in a series of jobs (using different executors per job)?

Just my thoughts, and happy to help out with more examples (I'm trying to move some CircleCI configuration with deploying Ruby functions with Serverless to using this orb).

**Describe alternatives you've considered**

**Additional context**