Run CI workflow on PRs even from forks

Author: goodboy

.github/workflows/ci.yml

@@ -1,12 +1,15 @@
 name: CI
 
 on:
-  # any time someone pushes a new branch to origin
+  # any time a new branch pushed to origin
   push:
 
-  # Allows you to run this workflow manually from the Actions tab
+  # to run workflow manually from the "Actions" tab
   workflow_dispatch:
 
+  # for on all (forked) PRs to repo
+  pull_request:
+
 jobs:
   # ------ sdist ------
   # test that we can generate a software distribution and install it