update howto release docs

Author: veenstrajelmer

docs/CONTRIBUTING.md

@@ -65,11 +65,12 @@
 ## Create release
 
 - make sure the `main` branch is up to date (check pytest warnings, important issues solved, all pullrequests and branches closed)
+- create and checkout branch for release
 - bump the versionnumber with `bumpversion minor`
 - update `docs/whats-new.md` and add a date to the current release heading
 - run local testbank with `pytest -m "not era5slow and not requireslocaldata"`
 - local check with: `python -m build` and `twine check dist/*` ([does not work on WCF](https://github.com/pypa/setuptools/issues/4133))
-- commit+push to github via PR
+- commit+push to branch and merge PR
 - copy the dfm_tools version from [pyproject.toml](https://github.com/Deltares/dfm_tools/blob/main/pyproject.toml) (e.g. `0.11.0`)
 - create a [new release](https://github.com/Deltares/dfm_tools/releases/new)
 - click `choose a tag` and type v+versionnumber (e.g. `v0.11.0`), click `create new tag: v0.11.0 on publish`