Different Double Slabs

This release is compatible with all versions 1.20.0 and up!*

*The only caveat is that the resource pack won't automatically have support for any new slabs added after 1.21.0, so message me on Discord reminding me to add them! (@owehttamy)

Changes:

• Fixed polished granite's double slab variant not rendering
• Fixed a significant mistake in mod support directions where I missed important details regarding support for column blocks and multiple other inconsistencies (Thanks @peow. on Discord!)
• Further elaborated on specific details in mod support directions to improve user understanding
• Updated the mod template model JSON to mirror the changes in the directions