Add v1 deprecation to v1 docs

[dontlaugh]

Hi everybody. Seems like you have a problem with the old jobs API. I run something like this

curl -X POST --header "Content-Type: application/json" -d '{
  "parallel": 1,
  "job": "deploy-tag",
  "build_parameters": {
    "VALUE": "40Mi"
  }
}' https://circleci.com/api/v1.1/project/github/paperlesspost/kubernetes-deployments/tree/master?circle-token=$CIRCLE_API_TOKEN

This has worked for months, until today. Got this response from the API

{"message":"An internal server error occurred."}

Started digging around and after some googling I saw the deprecation notice in a blog post:
https://circleci.com/blog/a-deprecation-notice-on-job-triggering-with-api-v1-1/

I would have commented in the forum, and tried to make an account, but it prompted me for 2FA. That's a bit much for your forum, imo.

Anyways, this is the API I've been using:

https://circleci.com/docs/api/#trigger-a-new-job

It would be helpful if the deprecation notice was there, as well. As far as I can tell, it's just on your blog.