How to migrate 'local notes' or 'on my mac' notes to iCloud? I've seen so many questions asked about it, and I found a proper solution today while working. See below. I searched around, and everyone's answer has been either 'copy all of your notes manually' or use a '3rd party solution'. This requires neither.
On Mac #1, I just transferred all my "Local Notes" into iCloud and can see them in Mac #2:


Click on "Local Notes" on left side of Notes window.  
Hit Command+A to Select All notes.
With mouse, drag all selected notes into "Notes" under "iCloud" on left side of Notes window.