Add circleCI config for building AMD64 image

[NicolasDorier]

You need to create a new CircleCI account, link to this project.

Then, go in the build environment variable of the project in CircleCI and setup:
DOCKERHUB_USER, DOCKERHUB_PASS, DOCKERHUB_REPO.

I advise you to have a dedicated account for docker hub different from your github account, and then give this account the rights to your dockerhub repo.

Then it could be:

DOCKERHUB_USER: jeffvandrewci
DOCKERHUB_PASS: mysecurepass
DOCKERHUB_REPO: jeffvandrewjr/btcqbo

Once you did this, tag git tag -a v0.1.0 -m v0.1.0, and push git push --tags.

If you messed up and want to do adjustement and retag..

1. Remove the tag git tag -d v0.1.0
2. Do your modifications and commit
3. Re add the tag git tag -a v0.1.0 -m v0.1.0
4. git push --tags --force