pull existing image before building, note reserved paths

.gitlab-ci.yml

@@ -19,6 +19,7 @@ variables:
     - mkdir /root/.docker
     - ln -s /secrets/docker /root/.docker/config.json
     - docker info
+    - docker pull ${IMAGE_TAG}:${CI_COMMIT_REF_SLUG} || true
   script:
     - cd ${IMAGE_DIR}
     - docker build -t ${IMAGE_TAG}:${CI_COMMIT_REF_SLUG} .

README.md

@@ -2,4 +2,15 @@
 
 These are dockerfiles maintained for third-party tools, languages, and the `apextoaster/base` utility image.
 
-To make pipelines and updates easy, these are in a monorepo. Make sure images build to the same hash (clean up caches).
+To make pipelines and updates easy, these are in a monorepo. Make sure images build to the same hash (clean up caches).
+
+## Cleanup
+
+Clean up `apt-get` with `apt-get autoclean && apt-get clean && rm -rf /var/lib/apt/lists/*`.
+
+## Paths
+
+`/build` and `/secrets` are reserved mount points for CI jobs.
+`/config` and `/data` are reserved mount points for runtime data.
+
+Tools that need an install directory should use `/<tool>`.