Add release doc (#125)

* Add releasing doc

* fix example link

Author: nmuesch

RELEASING.md

@@ -0,0 +1,33 @@
+# Releasing
+This document summarizes the process of doing a new release of this project.
+Release can only be performed by Datadog maintainers of this repository.
+
+## Schedule
+This project does not have a strict release schedule. However, we would make a release at least every 2 months.
+  - No release will be done if no changes got merged to the `master` branch during the above mentioned window.
+  - Releases may be done more frequently than the above mentioned window.
+
+## Make Sure Everything Works
+* Make sure tests are passing.
+  - Locally and in the continuous integration system.
+* Make sure documentation is up-to-date and building correctly.
+* Build the package locally (e.g. `python3 setup.py sdist`), install it into a fresh virtualenv and test the changes that have been made since the last release.
+
+## Release Process
+Our team will trigger the release pipeline.
+
+### Prerequisite 
+- Install [datadog_checks_dev](https://datadog-checks-base.readthedocs.io/en/latest/datadog_checks_dev.cli.html#installation) using Python 3.
+- Setup PyPI, see the internal documentation for more details
+
+### Update Changelog
+#### Commands
+- See changes ready for release by running `ddev release show changes .` at the root of this project. Add any missing labels to PRs if needed.
+- Run `ddev release changelog . <NEW_VERSION>` to update the `CHANGELOG.md` file at the root of this repository
+- Commit the changes to the repository in a release branch and open a PR. Do not merge yet.
+
+### Release
+1. Create the release on GitHub. [Example](https://github.com/DataDog/datadog-api-client-python/releases/tag/1.0.0b1)
+1. Checkout the tag created at the previous step.
+1. Run `ddev release build .` and `ddev release upload . `.
+   - Make sure that both an `sdist` and a [universal wheel](https://packaging.python.org/guides/distributing-packages-using-setuptools/#universal-wheels) have been uploaded to [PyPI](https://pypi.python.org/pypi/datadog/).