Replace asterisk with dash to appease markdownlint

Follow on/related to: !89 (merged)

The chart.sourcesList template we use in our readme template uses asterisks by default which elicits a stern warning from our markdown linter

Should be a quick fix to swap template for include, piped to a replace "*" "-"

include isn't natively supported in .gotmpl, so had to override the chart.sourcesList definition in _templates.gotmpl instead