Add: Jenkinsfile for CI validation

Currently runs two CIs, but this can be extended in the future

Jenkinsfile

@@ -0,0 +1,31 @@
+def ci_targets = [
+    ["linux-amd64", "openttd/compile-farm-ci:linux-amd64"],
+    ["linux-i386", "openttd/compile-farm-ci:linux-i386"],
+]
+def ci_stages = ci_targets.collectEntries {
+    ["${it[0]}" : generateCI(it[0], it[1])]
+}
+
+def generateCI(display_name, image_name) {
+    return {
+        dir("${display_name}") {
+            unstash "source"
+            docker.image("${image_name}").withRun("--volumes-from ${hostname} --workdir " + pwd()) { c->
+                sh "docker logs --follow ${c.id}"
+                sh "exit `docker wait ${c.id}`"
+            }
+        }
+    }
+}
+
+node {
+    stage("Checkout") {
+        checkout scm
+        stash name: "source", useDefaultExcludes: false
+    }
+
+    stage("CI") {
+        parallel ci_stages
+    }
+}
+