Update contributing info (#44)

CONTRIBUTING.md

@@ -61,3 +61,14 @@ GitHub [pull request](https://github.com/earth-system-radiation/pyRTE-RRTMTP/pul
 against the `main` branch.
 
 Pull Requests for new features should include tests and documentation.
+
+## How to Make a New Release?
+
+For maintainers:
+
+1. To make a new release, update the version number in `pyproject.toml` and `conda.recipe/meta.yaml`.
+2. Then, create a new release off the `main` branch on GitHub, using the "Draft a new release" button in [https://github.com/earth-system-radiation/pyRTE-RRTMGP/releases](https://github.com/earth-system-radiation/pyRTE-RRTMGP/releases).
+3. Create a new tag with the version number, and use the "Generate release notes" button to create the release notes.
+4. Review and update the the release notes as necessary, and publish the release and set it as the latest release.
+
+The documentation on [https://pyrte-rrtmgp.readthedocs.io/](https://pyrte-rrtmgp.readthedocs.io/) will update automatically.