Add .gitlab-ci.yml

.gitlab-ci.yml

+stages:
+  - build
+
+.build_template:
+  stage: build
+  tags:
+    - docker-build
+  script:
+    - python3 build-locally.py $CONFIG
+
+build_linux_64_python3.6.____cpython:
+  extends: .build_template
+  variables:
+    CONFIG: linux_64_python3.6.____cpython
+
+build_linux_64_python3.7.____cpython:
+  extends: .build_template
+  variables:
+    CONFIG: linux_64_python3.7.____cpython
+
+build_linux_64_python3.8.____cpython:
+  extends: .build_template
+  variables:
+    CONFIG: linux_64_python3.8.____cpython