Add README

Author: lsegal

README.md

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+# CodeBuilder Plugin for Jenkins
+
+This Jenkins plugin dynamically spins up cloud agents using AWS CodeBuild to
+execute jobs.
+
+## Usage
+
+Because permission management can be difficult, this plugin assumes you have
+created an AWS CodeBuild project with the necessary IAM roles for the job
+types that you will be running. The project can have any configuration; all
+settings will be overridden by the plugin to provide a build using source
+provided by the Jenkins host.
+
+Once a project is created, you can configure the cloud in Jenkins by adding
+a new cloud and configuring the plugin in `Manage Jenkins > Configure System`.
+After this, builds that match the cloud label will automatically be provisioned
+through AWS CodeBuild.
+
+### Quick Start
+
+#### Creating an AWS CodeBuild Project (Optional)
+
+If you have already setup a project, you can skip this step. Otherwise, if you
+want a quick way to bootstrap configuration, you can use the [AWS CLI][awscli]
+to create an AWS CodeBuild project with bare permissions by running the
+commands below:
+
+```sh
+# Optional command to create a bare IAM role named "jenkins-default"
+aws iam create-role \
+  --role-name jenkins-default \
+  --assume-role-policy-document \
+  '{"Version":"2012-10-17 ","Statement":[{"Effect": "Allow","Principal":{"Service":"codebuild.amazonaws.com"},"Action":"sts:AssumeRole"}]}'
+
+# Create the project named "jenkins-cluster" using our service role
+aws codebuild create-project \
+  --name jenkins-cluster \
+  --service-role jenkins-default \
+  --artifacts type=NO_ARTIFACTS \
+  --environment type=LINUX_CONTAINER,image=aws/codebuild/docker:18.09.0,computeType=BUILD_GENERAL1_SMALL \
+  --source $'type=NO_SOURCE,buildspec=version:0.2\nphases:\n  build:\n    commands:\n      - exit 1'
+```
+
+#### Configuring the Plugin
+
+In `Manage Jenkins > Configure System` you will find a drop-down to "Add a New
+Cloud":
+
+![Add a new cloud](docs/add-cloud.png)
+
+After adding the cloud, you can configure the region, project name, and
+other basic build agent details. Only region and project name are required.
+Credentials can be sourced from your `~/.aws/credentials` file or
+`AWS_ACCESS_KEY_ID` and `AWS_SECRET_ACCESS_KEY` environment variables if left
+blank.
+
+Your configuration might look something like this:
+
+![Configure the plugin](docs/configure.png)
+
+And that's it, you're all set to trigger new builds on AWS CodeBuild!
+
+[awscli]: https://docs.aws.amazon.com/cli/latest/userguide/cli-chap-install.html