Add gitlab-ci

.gitlab-ci.yml

+stages:
+  - build
+
+before_script:
+  - export DEBIAN_FRONTEND=noninteractive
+  - apt-get -y update
+  - apt-get -y install build-essential wget ca-certificates gnupg
+  - echo "deb http://ci.puri.sm/ scratch librem5" > /etc/apt/sources.list.d/ci.list
+  - wget -O- https://ci.puri.sm/ci-repo.key | apt-key add -
+  - apt-get -y update
+  - apt-get -y build-dep .
+
+build-debian-package:
+  image: debian:buster
+  tags:
+    - librem5
+  stage: build
+  script:
+    - dpkg-buildpackage -uc -us