Update README adding the CentOS Stream specific contributing section.

Merge Request Required Information

Summary of Changes

This MR is to update the README.md adding the contribution section. The motivation is to note our typical CentOS Stream specific use cases to test this repository not to forget. We can refer to the Fedora tests/ruby repository's README for the tests/ruby repository common information (tips). I also aligned the document style with the Fedora tests/ruby's README.md.

Approved Development Ticket(s)

All submissions to CentOS Stream must reference a ticket in Red Hat Jira.

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Please follow the CentOS Stream contribution documentation for how to file this ticket and have it approved.

List tickets each on their own line of this description using the format "Resolves: RHEL-76229", "Related: RHEL-76229" or "Reverts: RHEL-76229", as appropriate.