restore docs/upgrade_checklist.md

Author: carsonRadtke

docs/upgrade_checklist.md

@@ -0,0 +1,19 @@
+> When bumping the version, you need to update the following files:
+
+1. [ ] [CMakeLists.txt](../CMakeLists.txt) Bump `GSL_VERSION`
+1. [ ] [README.md](../README.md) Bump `GIT_TAG`
+1. [ ] [ios.yml](../.github/workflows/ios.yml) Bump `MACOSX_BUNDLE_BUNDLE_VERSION` and
+`MACOSX_BUNDLE_SHORT_VERSION_STRING`
+
+> After updating, you need to create a new GitHub release:
+
+1. [ ] [Microsoft/GSL - Create Release](https://github.com/microsoft/GSL/releases/new)
+
+Be sure to update the release notes accordingly and properly mention open-source
+contributors.
+
+> After a new release exists, update the `ms-gsl` vcpkg port:
+
+1. [ ] [Microsoft/vcpkg - ms-gsl port](https://github.com/microsoft/vcpkg/tree/master/ports/ms-gsl)
+
+Be sure to monitor the PR that updates the port for any feedback from vcpkg maintainers.