Clarify that pipelines work outside GCP except for specific functionality

[sarahmaddox]

In various places in the docs (e.g. the pipelines overview we state the following:

"Due to kubeflow/pipelines#345 and kubeflow/pipelines#337, Kubeflow Pipelines depends on Google Cloud Platform (GCP) services and some of the functionality is currently not supported by non-GKE clusters."

The documentation as it is worded today makes it seem like KFP can only work on GCP. However, due to the bugs listed above, only a couple non-essential pieces of functionality are unavailable outside GCP.

Update the docs to be more specific:

"Due to kubeflow/pipelines#345 and kubeflow/pipelines#337, a couple of non-critical pieces of functionality are currently available only on GKE clusters.

The code for the paragraph is in this shortcode (re-used in multiple places in the docs):
https://github.com/kubeflow/website/blob/master/layouts/shortcodes/pipelines-compatibility.html

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[sarahmaddox]

/cc iyera

[animeshsingh]

Did a quick PR on this #662

[sarahmaddox]

/close

[k8s-ci-robot]

@sarahmaddox: Closing this issue.

In response to this:

/close

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