Add GitLab CI support

.gitlab-ci.yml

+image: debian:stretch
+
+before_script:
+  - dpkg --add-architecture i386
+  - apt-get update
+  - apt-get install libx11-dev:i386 libc6-dev-i386 build-essential  -y
+
+smoke-test-by-make:
+  stage: build
+  script:
+    - make
+  tags:
+    - docker

README.md

 # Log
 
+[![pipeline status](https://git.iiens.net/brateau2015/diglog/badges/master/pipeline.svg)](https://git.iiens.net/brateau2015/diglog/commits/master)
+
 Log (diglog + analog) is a graphical environment for entering circuit schematics, and for analog 
 and digital circuit simulation. Please see [log/README](log/README) for more information.