Add additional HackerNews social guidelines

Why is this change being made?

Add additional content for Community Advocates to better understand HackerNews moderation rules.

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what