Rename "Artifact Storage" to "PipelineResource Storage" in install docs

The install docs aren't super clear about the meaning and purpose of "artifact storage".
Reading the existing doc it would be understandable if a user mistakenly
thought that Tekton relies on the storage configuration for all data in
and out of Tasks. In fact this storage is specific to PipelineResources
that are linked "from" one to another in a Pipeline.

This commit updates the docs to drop mention of "artifact storage" and
instead directly reference PipelineResources, with supporting links and
a note again warning of the alpha-ness of the feature.

docs/install.md

@@ -5,7 +5,7 @@ This guide explains how to install Tekton Pipelines. It covers the following top
 * [Before you begin](#before-you-begin)
 * [Installing Tekton Pipelines on Kubernetes](#installing-tekton-pipelines-on-kubernetes)
 * [Installing Tekton Pipelines on OpenShift](#installing-tekton-pipelines-on-openshift)
-* [Configuring artifact storage](#configuring-artifact-storage)
+* [Configuring PipelineResource storage](#configuring-pipelineresource-storage)
 * [Customizing basic execution parameters](#customizing-basic-execution-parameters)
 * [Creating a custom release of Tekton Pipelines](#creating-a-custom-release-of-tekton-pipelines)
 * [Next steps](#next-steps)
@@ -72,7 +72,7 @@ To install Tekton Pipelines on a Kubernetes cluster:
 
 Congratulations! You have successfully installed Tekton Pipelines on your Kubernetes cluster. Next, see the following topics:
 
-* [Configuring artifact storage](#configuring-artifact-storage) to set up artifact storage for Tekton Pipelines.
+* [Configuring PipelineResource storage](#configuring-pipelineresource-storage) to set up artifact storage for Tekton Pipelines.
 * [Customizing basic execution parameters](#customizing-basic-execution-parameters) if you need to customize your service account, timeout, or Pod template values.
 
 ### Installing Tekton Pipelines on OpenShift
@@ -117,22 +117,29 @@ for more information.
 
 Congratulations! You have successfully installed Tekton Pipelines on your OpenShift environment. Next, see the following topics:
 
-* [Configuring artifact storage](#configuring-artifact-storage) to set up artifact storage for Tekton Pipelines.
+* [Configuring PipelineResource storage](#configuring-pipelineresource-storage) to set up artifact storage for Tekton Pipelines.
 * [Customizing basic execution parameters](#customizing-basic-execution-parameters) if you need to customize your service account, timeout, or Pod template values.
 
 If you want to run OpenShift 4.x on your laptop (or desktop), you
 should take a look at [Red Hat CodeReady Containers](https://github.com/code-ready/crc).
 
-## Configuring artifact storage
+## Configuring PipelineResource storage
 
-`Tasks` in Tekton Pipelines need to ingest inputs from and store outputs to one or more common locations.
- You can use one of the following solutions to set up resource storage for Tekton Pipelines:
+PipelineResources are one of the ways that Tekton passes data between Tasks. If you intend to
+use PipelineResources in your Pipelines then you'll need to configure a storage location
+for that data to be put so that it can be shared between Tasks in the Pipeline.
+
+**Note:** Pipeline Resources are in alpha and are currently undergoing considerable redesign. Therefore
+this storage configuration is possibly going to change in future. Writing Tasks and Pipelines today that rely
+on this feature may mean you'll need to rewrite those Tasks and Pipelines when the redesign is complete. See
+the [explanation for the redesign in the PipelineResources doc](./resources.md#why-arent-pipelineresources-in-beta)
+and [issue 1673](https://github.com/tektoncd/pipeline/issues/1673) to follow along with the redesign work.
+
+The storage options available for sharing PipelineResources between Tasks in a Pipeline are:
 
   * [A persistent volume](#configuring-a-persistent-volume)
   * [A cloud storage bucket](#configuring-a-cloud-storage-bucket)
 
-**Note:** Inputs and output locations for `Tasks` are defined via [`PipelineResources`](https://github.com/tektoncd/pipeline/blob/master/docs/resources.md).
-
 Either option provides the same functionality to Tekton Pipelines. Choose the option that
 best suits your business needs. For example: