Adds notes to Connector clients and Connectors page

[kosabogi]

Overview

This PR adds notes to the Connector clients and Connectors pages to provide users with more context about the content of these pages.

Related issue

#98

Preview

Connector clients
Connectors

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[leemthompo]

LGTM with one suggestion for accessibility. We still have lots of instances of "See" across our docs, but "Refer to" is the preferred alternative :)