update checklist for new pull requests (#288)

* update checklist for new pull requests

* reorder checkboxes to accomodate internal library changes

* reword public API to downstream API

.github/pull_request_template.md

@@ -12,14 +12,19 @@ Closes #
 
 This PR addresses ...
 
-**Checklist**
-
-- [ ] for a public change, added a towncrier news fragment in `changes/`: <details><summary>`echo "changed something" > changes/<PR#>.<changetype>.rst`</summary>
-
-    - ``changes/<PR#>.apichange.rst``: change to public API
-    - ``changes/<PR#>.bugfix.rst``: fixes an issue
-    - ``changes/<PR#>.general.rst``: infrastructure or miscellaneous change
-- [ ] updated relevant tests
-- [ ] updated relevant documentation
-- [ ] updated relevant milestone(s)
-- [ ] added relevant label(s)
+<!-- if you can't perform these tasks due to permissions, please ask a maintainer to do them -->
+## Tasks
+- [ ] update or add relevant tests
+- [ ] update relevant docstrings and / or `docs/` page
+- [ ] Does this PR change any API used downstream? (if not, label with `no-changelog-entry-needed`)
+  - [ ] write news fragment(s) in `changes/`: `echo "changed something" > changes/<PR#>.<changetype>.rst` (see below for change types)
+  - [ ] run regression tests with this branch installed (`"git+https://github.com/<fork>/stcal@<branch>"`)
+    - [ ] [`jwst` regression test](https://github.com/spacetelescope/RegressionTests/actions/workflows/jwst.yml) 
+    - [ ] [`romancal` regression test](https://github.com/spacetelescope/RegressionTests/actions/workflows/romancal.yml)
+
+<details><summary>news fragment change types...</summary>
+
+- ``changes/<PR#>.apichange.rst``: change to public API
+- ``changes/<PR#>.bugfix.rst``: fixes an issue
+- ``changes/<PR#>.general.rst``: infrastructure or miscellaneous change
+</details>