[DOCS] Add the Receptor Getting Started Guide on RTD

[tvo318]

Feature type

Doc enhancement.

Feature Summary

Create a Getting Started Guide for the Receptor docs from the following sources:

• Google docs draft from @thom-at-redhat
• Clustering content from AWX

Select the relevant components

• Docs

Steps to reproduce

1. Clone receptor docs repo.
2. Add getting_started.rst content from the Google docs draft
3. Open a PR and make updates and revisions to the rst file only, discontinue updates/revision to the [Google docs draft] (https://docs.google.com/document/d/1hGCfWE1U0ZFipzWdFO56A8jrCvAjoeYbaYjLKGpM1IQ/edit#heading=h.z5xrlcfkx1cs)

Current results

No Getting Started Guide in https://ansible.readthedocs.io/projects/receptor/en/latest/index.html

Suggested feature result

Getting Started Guide on RTD published.

Additional information

Addresses the ask for AAP-16722