Add link to plugin that creates a stacked percentage chart

Author: y-takey

docs/developers/plugins.md

@@ -7,6 +7,7 @@ Plugins are the most efficient way to customize or change the default behavior o
  - <a href="https://github.com/chartjs/chartjs-plugin-annotation" target="_blank">chartjs-plugin-annotation.js</a> - Draw lines and boxes on chart area.
  - <a href="https://github.com/chartjs/chartjs-plugin-deferred" target="_blank">chartjs-plugin-deferred.js</a> - Defer initial chart update until chart scrolls into viewport.
  - <a href="https://github.com/compwright/chartjs-plugin-draggable" target="_blank">chartjs-plugin-draggable.js</a> - Makes select chart elements draggable with the mouse.
+ - <a href="https://github.com/y-takey/chartjs-plugin-stacked100" target="_blank">chartjs-plugin-stacked100.js</a> - Draw 100% stacked bar chart.
  - <a href="https://github.com/chartjs/chartjs-plugin-zoom" target="_blank">chartjs-plugin-zoom.js</a> - Enable zooming and panning on charts.
  - <a href="https://github.com/chartjs/Chart.BarFunnel.js" target="_blank">Chart.BarFunnel.js</a> - Adds a bar funnel chart type.
  - <a href="https://github.com/chartjs/Chart.LinearGauge.js" target="_blank">Chart.LinearGauge.js</a> - Adds a linear gauge chart type.