Offering CodeBlock line number feature from CodiMD (a flavour of Markdown - The free Open Source version of HackMD) would be nice.
The usecase is straigth forward:
If you want to show line numbers in the Code-Block of your document and to be able to specify the line number it starts from.
See also: https://codimd.web.cern.ch/features?both#Code-Block
Then type = after specifying the code block languagues. Also, you can specify the start line number. Like below, the line number starts from 101: