Update after-version-bump description

bin/after-version-bump.js

@@ -4,6 +4,9 @@
 // but _before_ it commits, so we have time to update the
 // version numbers throughout the repo and add it to the
 // release commit.
+// After updating version numbers, this runs a full
+// IS_RELEASE_BUILD=1 build, so that the version numbers
+// are properly embedded in the JS bundles.
 // NOTE this _amends_ the previous commit, which should
 // already be a "Release" commit generated by bin/release.