Updated Docker image build on CircleCI (markdown)

Docker-image-build-on-CircleCI.md

@@ -4,8 +4,6 @@ For those who used to work with the docker image build process, we’ve migrated
 
 
 The config of docker image  now live at https://github.com/pytorch/pytorch/tree/master/.circleci/docker 
-And we have weekly jobs to rebuild all the images:  https://github.com/pytorch/pytorch/blob/master/.circleci/config.yml#L5695-L5751  (this link might not work if we ever update config.yml file, so please search for “docker_build_job” to be sure)
-
 and you can find existing images (both permanent and weekly) at [http://docker.pytorch.org](http://docker.pytorch.org/)  which will be updated hourly by this job: https://github.com/pytorch/pytorch/blob/master/.circleci/config.yml#L5752-L5776 (for same reason as above, you can search “ecr_gc_job” to be sure)
 
 
@@ -13,7 +11,9 @@ and you can find existing images (both permanent and weekly) at [http://docker.p
 
 ### How to trigger new build process if I don’t want to wait for a week?
 
-Comment out or remove https://github.com/pytorch/pytorch/blob/cb9029df9db397f66da234d21b5ddafd6be6e602/.circleci/generate_config_yml.py#L120-L127, so your PR can/will trigger build job. **REMEMBER** to run [regenerate.sh](https://github.com/pytorch/pytorch/blob/master/.circleci/regenerate.sh) when you’re inside .circle directory after you update the file.
+New images are automatically built when any changes are committed to `.circleci/docker`. Developer images are retained for 2 weeks, so if your builds are older than 2 weeks you will need to rebuild your images if you intend to merge the PR associated with docker image changes.
+
+New images will automatically be passed down through to dependent jobs.
 
 ### Where to find tags for newly created/pushed images?
 
@@ -24,12 +24,6 @@ Comment out or remove https://github.com/pytorch/pytorch/blob/cb9029df9db397f66d
 We have ecr_gc_job job (you can search for it in config.yml) that runs every hour to purge old images. Currently, we need temporary images for 1 day, and weekly builds for 2 weeks. And we will keep image with tags defined in https://github.com/pytorch/pytorch/blob/master/.circleci/verbatim-sources/workflows-ecr-gc.yml#L13 forever. 
 code for the purge job is https://github.com/pytorch/pytorch/blob/master/.circleci/ecr_gc_docker/gc.py 
 
-### How to use new images?
-
-1. locate new image tag at http://docker.pytorch.org/pytorch.html
-2. test with new images, you need to update https://github.com/pytorch/pytorch/blob/master/.circleci/cimodel/data/pytorch_build_definitions.py#L16 (or search for DOCKER_IMAGE_VERSION) and regenerate config.yml
-3. update  https://github.com/pytorch/pytorch/blob/master/.circleci/verbatim-sources/workflows-ecr-gc.yml#L13  and land changes to make sure the images won’t be purged
-
 ### The production images disappeared, what should I do?
 
 Sometimes there is a bug in ecr_gc_job and it deletes Docker images it shouldn't. All Docker images are also saved to S3 with a one month retention period, so there's a chance they may still be there.  You can use this script to recover in that case:
@@ -82,7 +76,6 @@ Note this instruction provides guidance to add a new **base** docker image. If y
 - Test your image by building it locally.
 - Add a repo in AWS ECR to hold your image. It requires access to PyTorch's AWS account to do this step.
 - Trigger a new build process as described above.
-- Remove https://github.com/pytorch/pytorch/blob/master/.circleci/verbatim-sources/workflows-ecr-gc.yml#L2-L8 so that docker_hub_index_job can be run on your PR. http://docker.pytorch.org/ will then display images pushed into the newly created repo.
 - **WAIT UNTIL ALL BUILD JOBS TO FINISH** and make sure all new images have been uploaded. Save the tag of the new images.
 - Run regenerated.sh with the new tag and update your PR.