Stage more links

doc/continuous_integration/codecov.md

@@ -1 +1,3 @@
-https://codecov.io/gh/ros-planning/navigation2
+https://codecov.io/gh/ros-planning/navigation2
+
+https://docs.codecov.io/docs/codecov-yaml

doc/continuous_integration/dockerfile.md

@@ -0,0 +1,33 @@
+Dockerfiles are 
+
+configured via the [Dockerfile](/Dockerfile) yaml file within the `.circleci/` folder at the root of the GitHub repo. Further references on configuring CircleCI, such as syntax and structure can be found here:
+
+* https://circleci.com/docs/2.0/writing-yaml
+* https://circleci.com/docs/2.0/configuration-reference
+
+https://docs.docker.com/engine/reference/builder/
+
+
+* https://hub.docker.com/_/ros
+* https://github.com/osrf/docker_images
+
+
+* [colcon](https://colcon.readthedocs.io/en/released)
+  * CLI tool to build sets of software packages
+* [rosdep](http://wiki.ros.org/rosdep)
+  * CLI tool for installing system dependencies
+* [vcstool](https://github.com/dirk-thomas/vcstool)
+  * CLI for working with multiple repositories easier
+
+
+
+* [ccache](https://ccache.dev)
+  * Compiler cache for speeding up recompilation
+* [lcov](http://ltp.sourceforge.net/coverage/lcov.php)
+  * Front-end for GCC's coverage testing tool gcov
+
+* https://docs.docker.com/develop/develop-images/build_enhancements/
+* https://github.com/moby/buildkit
+
+
+[cache apt packages](https://github.com/moby/buildkit/blob/master/frontend/dockerfile/docs/experimental.md#example-cache-apt-packages) to avoid unnecessarily re-downloading the same packages from over the network, even if the docker image layer cache for that directive in the Dockerfile is busted.

doc/continuous_integration/dockerhub.md

@@ -1 +1,14 @@
-https://hub.docker.com/r/rosplanning/navigation2
+https://hub.docker.com
+
+https://hub.docker.com/r/rosplanning/navigation2
+
+
+
+
+
+https://docs.docker.com/docker-hub/builds
+https://docs.docker.com/docker-hub/builds/advanced
+
+https://docs.docker.com/docker-hub/webhooks
+
+[example](https://github.com/osrf/docker_images/blob/master/.github/workflows/trigger_nightly.yaml)