Document release process of docker-machine

The process is not complex but it's not very well known to anyone. This
issue template documents the whole process which gives an option to
improve and iterate over it.

.gitlab/issue_templates/Release.md

+For visioning we use `X.Y.Z-gitlab.G` pattern, where:
+
+- `X.Y.Z` is directly taken from the upstream version. For now we add
+  all our changes on top of `0.16.2` which is the last stable tag of
+  Docker Machine.
+- `G` is the incremental number increased for each of our releases.
+
+### Release 0.16.2-gitlab.{{G}}
+
+- [ ] `git checkout master && git pull`
+- [ ] Increment the value of {{G}} but checking the value defined in https://gitlab.com/gitlab-org/ci-cd/docker-machine/-/blob/master/version/version.go#L9.
+- [ ] Update [version/version.go](https://gitlab.com/gitlab-org/ci-cd/docker-machine/-/blob/93376765782dc284064f3e4ccf87d8500e983888/version/version.go#L9) to `0.16.2-gitlab.{{G}}`.
+- [ ] Add file `git add version/version.go`
+- [ ] Commit `git commit -m "Bump version to 0.16.2-gitlab.{{G}}"`
+- [ ] Create git tag `git tag -s 0.16.2-gitlab.{{G}} -m "Version 0.16.2-gitlab.{{G}}`
+- [ ] Push tag `git push origin 0.16.2-gitlab.{{G}}`
+- [ ] Push to master `git push origin master`