Release process and auto-trgiggers

[ChihChengLiang]

ethereum/eth2.0-tests#22 discuss the process of reflecting a merged PR in the "eth2.0-test-generators" repo to the "eth2.0-tests" repo.

One proposed way is to auto trigger the update whenever a PR is merged. The issue is that it's difficult for the machine to know whether to bump a major version or a minor version.

After an offline discussion with @jannikluhn, we propose to manually release immediately every time a PR is merged.