chore: add README

Signed-off-by: Keith Zantow <[email protected]>

README.md

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+# go-collections
+
+[![Go Report Card](https://goreportcard.com/badge/github.com/anchore/go-collections)](https://goreportcard.com/report/github.com/anchore/go-collections)
+[![GitHub go.mod Go version](https://img.shields.io/github/go-mod/go-version/anchore/go-collections.svg)](https://github.com/anchore/go-collections)
+[![License: Apache-2.0](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](https://github.com/anchore/go-collections/blob/main/LICENSE)
+[![Slack Invite](https://img.shields.io/badge/Slack-Join-blue?logo=slack)](https://anchore.com/slack)
+
+A library with generic data structures for common collection operations.
+
+## Status
+
+***Consider this project to be in alpha. The API is not stable and may change at any time.***
+
+## Overview
+
+`collections.TaggedValue` a set of tags associated with a value
+
+`collections.TaggedValueSet` provides methods for performing set operations on an arbitrary set of tagged values