This is the most basic “index.html” template for running “.pde” sketches under Pjs:
<script defer src=http://CDN.JSDelivr.net/processing.js/latest></script>
<canvas data-processing-sources=sketch.pde></canvas>
Just replace the “sketch.pde” w/ the actual name of your “.pde” file.
Here’s an online example: 
https://GoSubRoutine.GitHub.io/Grumbo/Grumbo_Adventure_OOP/Grumbo_Adventure/
And its corresponding “index.html” file:
For multiple “.pde” files for the same sketch, just place them all after data-processing-sources=", separating each 1 w/ a space: 
And its corresponding multiple “.pde” sketch:
https://GoSubRoutine.GitHub.io/Grumbo/Grumbo_Adventure_OOP/