Add detail about building docker images locally

[kerchner]

Update https://sfm.readthedocs.io/en/stable/development.html#building-vs-pulling and/or provide an example.dev.docker-compose.yml as part of the sfm-docker repo, to contain information along the lines of (thanks @lwrubel ):

If you're changing a Dockerfile or even the scripts referenced there (such as invoke.sh), I think it needs to be rebuilt. You can use the build statement in the docker-compose, like you said. You can also then add a --build flag to docker-compose up -d in order to force the build the next time, even if there is already an image saved from a previous local build.

   build:
       context: ../sfm-twitter-harvester
       dockerfile: Dockerfile-rest-harvester

docker-compose up -d --build
or
docker-compose build --no-cache
docker-compose up -d

[lwrubel]

Note that if the sfm-base image (or the setup_reqs.sh it references) is changed and the sfm-base image is locally built, that copy will not get used when referenced in other Dockerfiles, since they refer to a particular sfm-base digest.