I've been doing something similar for 20+ years at: https://github.com/nickjj/notes

    - Running `notes` will open this month's notes for YYYY_MM.txt in your default $EDITOR
    - Running `notes hello world` will append `hello world` to YYYY_MM.txt
    - Running `$stdout | notes` will append another program's output to YYYY_MM.txt (useful for piping your clipboard)

I find this offers the least amount of resistance for quickly adding notes. Every method of input is 2 seconds away on the terminal and grep makes things searchable enough where I can still pull things out from files 5-10 years ago without issues.

I tried YYYY_MM_DD.txt for a while but I found it to be too fragmented. Oftentimes I want to look at a few day's worth of notes at a glance.