add ci script

.gitlab-ci.yml

+build_esp8266_image:
+  stage: build
+  image: python:3
+  before_script:
+    - pip install -U platformio
+  script:
+    - pio run
+    - mv .pio/build/mks_robin_nano35/Robin_nano35.bin Robin_nano35.bin
+  artifacts:
+    paths:
+      - Robin_nano35.bin