Update .github/workflows/update-subtree.yml

Co-authored-by: Carolyn Zech <[email protected]>

.github/workflows/update-subtree.yml

@@ -51,7 +51,7 @@ jobs:
 
         # subtree/library has the subtree-split variant of a commit that previously
         # went into upstream/master. Running `git subtree split` on top of the
-        # original commit is much faster (my experiment when working on 280k+
+        # original commit (i.e., the commit from upstream/master) is much faster (my experiment when working on 280k+
         # commits: 113 seconds vs 613 seconds) than using the HEAD commit from
         # subtree/library as base.
         SUBTREE_HEAD=$(git log --format=%s -n 1 origin/subtree/library)