ToC table of content tag could display other than 3 levels

[tai271828]

Is your feature request related to a problem? Please describe. Feature request.

Describe the solution you'd like This feature is implemented in codimd already https://github.com/hackmdio/codimd/pull/1532 . Let's wish this feature will be deployed or ported to hackmd.io soon : D

Additional context There is an open issue in Chinese https://github.com/hackmdio/hackmd-io-issues/issues/177 . Let me report the same feature request in English to see what the other users speaking in other languages think about.