add .md file extensions

[whysthatso]

as you currently use markdown syntax, this might help sync / edit the file on other devices. or make the filename customizable.

my use case: i sync the file with resilio and make it available on my phone, where markdown editors are wqorking quite nicely, but most of them will ignore files that do not have .md extensions...

equivalent if you ever decide to support todolist.txt syntax, then the file should have .txt extension.

if it's not too disruptive of an update process...

[FederAndInk]

You can change the filename: