Add a RELEASE.md file

Add a RELEASE.md file describing the release process.

Author: Éric Lemoine

RELEASE.md

@@ -0,0 +1,16 @@
+# Release
+
+Steps for releasing a new version of Pointcloud.
+
+Add a new section to the [NEWS](NEWS) file, listing all the changes associated with the new release.
+
+Change the version number in the [Version.config](Version.config) and
+[pgsql/expected/pointcloud.out](pgsql/expected/pointcloud.out) files.
+
+Create a PR with these changes. When the PR is merged create a tag for the new release and push
+it to GitHub:
+
+```bash
+$ git tag -a x.y.z -m 'version x.y.z'
+$ git push origin x.y.z
+```