Update the doc content creation instructions

[dwelsch-esi]

Make changes to improve the effectiveness of the KEDA documentation contributor instructions.

Use-Case

Contributors, especially documentation contributors, might have trouble finding the information they need to get started.

Specification

Make the following changes to the keda-docs README:

• Move the "Become a listed KEDA user!" and "Become a listed KEDA commercial offering!" sections into their own files, or move them to the bottom of the README, so they're not at the top of the keda-docs README.
• Combine "Adding scaler documentation" and "Writing documentation for a scaler" so that they're not separated by "Writing documentation for a new authentication provider".

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 7 days if no further activity occurs. Thank you for your contributions.

[nate-double-u]

It's best not to auto-delete this issue; it is still relevant.