Minimally document chart publishing in README

chart/README.md

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+# Flux chart
+
+This directory contains a chart for flux. See [the README.md there](./flux/README.md) for
+instructions on how to use it.
+
+## Publishing new charts
+
+We use GitHub pages to publish the chart as a versioned package. The
+tarballs and index.yaml file are updated with a script in that branch.