release: Add release.yaml

`release.yaml` contains `github_tag`. `github_tag` is updated everytime we
make a new `lambda-linux-vbox.iso` release.

We also edit `README.md` as required.

Author: rajivr

release/release.yaml

@@ -0,0 +1,6 @@
+github_tag: v1703.0.0
+github_user: lambda-linux
+github_repo: lambda-linux-vbox
+docker: v1.12.6
+kernel: v4.9.20
+vbox_guest_additions: v5.1.20