Feature/mad 91 gitlab pipeline

Gitlab pipeline definition for build, test + deploy. README updated with relevant information + description of steps for running the same jobs locally. Feel free to edit the README as you see fit.

.gitlab-ci.yml

@@ -36,7 +36,7 @@ test:
 deploy:
     stage: deploy
     only: 
-        - feature/mad-91-gitlab-pipeline
+        - main
     tags:
         - vips-runner
     script: