Update validation README to address unresolved review issues

[Rene2mt]

This is a ...

fix - something needs to be different

This relates to ...

• the FedRAMP OSCAL Registry
• the FedRAMP OSCAL baselines
• the Guide to OSCAL-based FedRAMP Content
• the Guide to OSCAL-based FedRAMP System Security Plans (SSP)
• the Guide to OSCAL-based FedRAMP Security Assessment Plans (SAP)
• the Guide to OSCAL-based FedRAMP Security Assessment Results (SAR)
• the Guide to OSCAL-based FedRAMP Plan of Action and Milestones (POA&M)
• the FedRAMP SSP OSCAL Template (JSON or XML Format)
• the FedRAMP SAP OSCAL Template (JSON or XML Format)
• the FedRAMP SAR OSCAL Template (JSON or XML Format)
• the FedRAMP POA&M OSCAL Template (JSON or XML Format)

User Story

As a FedRAMP OSCAL practitioner, I need clear instructions on how to validate my FedRAMP OSCAL content locally, so that it meets FedRAMP expectations when submitted.

The existing README is the initial release of these instructions and needs to be updated to address prior review comments from PR #636

Goals

Address the following unresolved comments from PR #636:

• Add README.md to OSCAL CLI instructions #636 (comment)
• OSCAL-CLI offers both zip and tar.gz. Update instructions so its valid for either Linux or Windows users (Add README.md to OSCAL CLI instructions #636 (comment))
• Add README.md to OSCAL CLI instructions #636 (comment)
• Add README.md to OSCAL CLI instructions #636 (comment)
• Add README.md to OSCAL CLI instructions #636 (comment)
• Add README.md to OSCAL CLI instructions #636 (comment)

Dependencies

No response

Acceptance Criteria

• All FedRAMP Documents Related to OSCAL Adoption (https://github.com/GSA/fedramp-automation) affected by the changes in this issue have been updated.
• A Pull Request (PR) is submitted that fully addresses the goals of this User Story. This issue is referenced in the PR.

Other information

No response

[aj-stein-gsa]

Sorry, I reopened #629. I had missed that this issue was open up specifically for feedback.