(#506) Add docs about not using private variables

[AdmiringWorm]

Description Of Changes

This pull request adds some basic documentation for the new rule that will be included in the next / future version of the package validator to give some information about why the rule flagged the package, what can be done to unflag the package and why it was flagged.

Motivation and Context

Need to document any new rules that gets added to the validator.

Testing

• [x] I have previewed these changes using the Docker Container or another method before submitting this pull request.

Change Types Made

• [ ] Minor documentation fix (typos etc.).
• [ ] Major documentation change (refactoring, reformatting or adding documentation to existing page).
• [x] New documentation page added.

Change Checklist

• [ ] Requires a change to menu structure (top or left hand side)/
• [ ] Menu structure has been updated

Related Issue

Fixes #506

[gep13]

@AdmiringWorm this looks good to me, we can get this merged in once we are ready to ship the next round of Package Moderation Services.