templates: minor improvements

Link to GitHub release creation form.  Update path to download page.

Author: bgilbert

.github/ISSUE_TEMPLATE/python-bump.md

@@ -8,4 +8,4 @@
 - [ ] Upload new wheels to [GitHub release](https://github.com/openslide/openslide-python/releases)
 - [ ] [Download new AppVeyor YAML](https://ci.appveyor.com/project/OpenSlide/openslide-python/settings/yaml) and commit it to `openslide-automation/appveyor/openslide-python.yml`
 - [ ] Update MacPorts package
-- [ ] Update website: Python 3 versions in `download/index.markdown`
+- [ ] Update website: Python 3 versions in `download/index.md`

.github/ISSUE_TEMPLATE/release.md

@@ -8,7 +8,7 @@
 - [ ] `python setup.py register sdist`
 - [ ] `twine upload dist/*`
 - [ ] Recompress tarball with `xz`
-- [ ] Attach release notes to [GitHub release](https://github.com/openslide/openslide-python/releases); upload tarballs and wheels
+- [ ] Attach release notes to [GitHub release](https://github.com/openslide/openslide-python/releases/new); upload tarballs and wheels
 - [ ] `python setup.py build_sphinx` and copy `build/sphinx/html/` to website `api/python/`
 - [ ] Update website: `_data/releases.yaml`, `_includes/news.markdown`
 - [ ] Send mail to -announce and -users