added gitlab-ci from cross wiki

.gitlab-ci.yml

@@ -0,0 +1,14 @@
+variables:
+    # the host where the docker instance is running
+    DOCKER_HOST: tcp://docker:2375/
+    # use for much faster builds
+    DOCKER_DRIVER: overlay2
+    # ensure cross knows it's running remotely
+    CROSS_REMOTE: 1
+
+services:
+    - docker:18.09-dind
+
+armv6:
+    script:
+        - cross test --target arm-unknown-linux-gnueabihf