Implement support for remaining block types

[johndgiese]

• Review the blocks code here https://github.com/innolitics/n2y/blob/main/n2y/blocks.py#L457-L491
• Update the README table to add any relevant notes for the various block types
• Every block type should be in the table
• Only add information that is not obvious; e.g., if an paragraph block just makes a paragraph in markdown, we don't need to add any comment about it.
• For blocks that haven't yet been implemented, write out how you think they should work in the readme table; e.g., the Pdf block can download the PDF to the "media root" and add a link in the GitHub to the downloaded PDF file.
• Assign a PR to @bimbashrestha for him to review. The PR should ONLY contain changes to the README at this point
• Once Bimba approves the direction, implement the proposed changes.

[sHermanGriffiths]

Addressed with PR #65