Write a new Tekton Triggers Overview

Write a new Tekton Triggers Overview that explains at a high-level what Triggers is, how it works, and what you can do with it.

docs/README.md

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-title: "Triggers and EventListeners"
-linkTitle: "Triggers"
+title: "Overview of Tekton Triggers"
+linkTitle: "Overview"
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-  Event Triggers
+  Tekton Triggers
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   github_project_repo: https://github.com/tektoncd/triggers
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-# Tekton Triggers
 
-Triggers enables users to map fields from an event payload into resource
-templates. Put another way, this allows events to both model and instantiate
-themselves as Kubernetes resources. In the case of `tektoncd/pipeline`, this
-makes it easy to encapsulate configuration into `PipelineRun`s and
-`PipelineResource`s.
+# Overview of Tekton Triggers
 
-![TriggerFlow](https://github.com/tektoncd/triggers/blob/master/images/TriggerFlow.png?raw=true)
+Tekton Triggers is a Tekton component that allows you to detect and extract information from events from a variety of sources and deterministically instantiate
+and execute [`TaskRuns`](https://github.com/tektoncd/pipeline/blob/master/docs/taskruns.md) and [`PipelineRuns`](https://github.com/tektoncd/pipeline/blob/master/docs/pipelineruns.md)
+based on that information. Tekton Triggers can also pass information extracted from events directly to `TaskRuns` and `PipelineRuns`. You install Tekton Triggers on your Kubernetes
+cluster as an extension to Tekton Pipelines.
 
-## Learn More
+## How does Triggers work?
 
-See the following links for more on each of the resources involved:
+Tekton Triggers consists of a controller service that runs on your Kubernetes cluster as well as the following Kubernetes Custom Resource Definitions (CRDs) that extend
+the functionality of Tekton Pipelines to support events:
 
-- [`TriggerTemplate`](triggertemplates.md)
-- [`TriggerBinding`](triggerbindings.md)
-- [`EventListener`](eventlisteners.md)
-- [`ClusterTriggerBinding`](clustertriggerbindings.md)
+*  [`EventListener`](https://github.com/tektoncd/triggers/blob/master/docs/eventlisteners.md) - listens for events at a specified port on your Kubernetes cluster.
+   Specifies one or more `Triggers`.
 
+*  [`Trigger`](https://github.com/tektoncd/triggers/blob/master/docs/triggers.md) - specifies what happens when the `EventListener` detects an event. A `Trigger` specifies
+   a `TriggerTemplate`, a `TriggerBinding`, and optionally, an `Interceptor`.
+
+*  [`TriggerTemplate`](https://github.com/tektoncd/triggers/blob/master/docs/triggertemplates.md) - specifies a template for the `TaskRun` or `PipelineRun` you want to
+   instantiate and execute when EventListener detects an event.
+
+*  [`TriggerBinding`](https://github.com/tektoncd/triggers/blob/master/docs/triggerbindings.md) - specifies the fields in the event payload from which you want to extract
+   data as well as the fields in your `TaskRun` or `PipelineRun` to populate with the extracted values. In other words, it *binds* payload fields to `TaskRun` or
+   `PipelineRun` fields.
+
+*  [`ClusterTriggerBinding`](https://github.com/tektoncd/triggers/blob/master/docs/clustertriggerbindings.md) - a cluster-scoped version of the `TriggerBinding`,
+   especially useful for reuse within your cluster.
+
+*  [`Interceptor`](https://github.com/tektoncd/triggers/blob/master/docs/eventlisteners.md#interceptors) - a "catch-all" event processor for a specific platform that
+   runs before the `TriggerBinding` enabling you to perform payload filtering, verification (using a secret), transformation, define and test trigger conditions, and other
+   useful processing. Once the event data passes through an interceptor, it then goes to the `Trigger` before you pass the payload data to the `TriggerBinding`.
+
+   **Note:** `Interceptors` are currently part of `EventListeners` but are being converted to a standalond CRD in [PR 960](https://github.com/tektoncd/triggers/pull/960). 
+
+
+## What can I do with Triggers?
+
+As an example, you can implement the following CI/CD workflow with Triggers:
+
+1. Triggers listens for a git commit or a git pull request event. When it detects one, it executes a unit test [`Pipeline`](https://github.com/tektoncd/pipeline/blob/master/docs/pipelines.md) on the committed code.
+
+2. Triggers listens for a git push event indicating the test finished successfully. When it detects one, it validates the test's outcome and executes a `Pipeline` that builds the tested code.
+
+3. When the associated `PipelineRun` completes execution, Triggers checks the outcome of the build, and if it's successful, executes a [`Task`](https://github.com/tektoncd/pipeline/blob/master/docs/tasks.md) that uploads the build artifacts to the Docker registry of your choice.
+
+4. Finally, the Docker registry sends an event to [Pub/Sub](https://cloud.google.com/pubsub/docs/overview), which triggers a `Pipeline` that pushes the build artifacts to a staging environment.
+
+
+## Further Reading
+
+To get started with Tekton Triggers, see the following:
+
+*   [Setting Up Tekton Triggers](https://github.com/tektoncd/triggers/blob/master/docs/install.md)
+*   [Getting Started with Tekton Triggers](https://github.com/tektoncd/triggers/blob/master/docs/getting-started/README.md)
+*   [Tekton Triggers code examples](https://github.com/tektoncd/triggers/tree/master/examples)