Add .gitlab-ci.yml

.gitlab-ci.yml

+before_script:
+  - '[[ -d /home/piphone/build ]] || mkdir -p /home/piphone/build'
+
+job install:
+  script:
+    - '[[ -d /srv/piphone/sip_backend ]] || mkdir -p /srv/piphone/sip_backend'
+    - (cd /srv/piphone/sip_backend && git clone $CI_BUILD_REPO)
+  stages:
+    - install
+  cache:
+    untracked: true
+  tags:
+    - piphone
+    - ssh
+  only:
+    - master
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