add info about github reactions

Author: etpinard

CONTRIBUTING.md

@@ -10,9 +10,12 @@ Bug reports must be accompanied with a reproducible example. We recommend using
 [jsbin](https://jsbin.com) to share your example.
 
 Note that GitHub issues are reserved for bug reports and feature requests only.
-Implementation questions should be asked on Stack Overflow (tagged
-[`plotly`](https://stackoverflow.com/questions/tagged/plotly)) or on
-community.plot.ly (tagged [`plotly-js`](http://community.plot.ly/c/plotly-js)).
+Implementation questions should be asked on)
+community.plot.ly (tagged [`plotly-js`](http://community.plot.ly/c/plotly-js)) or on Stack Overflow (tagged
+[`plotly`](https://stackoverflow.com/questions/tagged/plotly).
+
+Comments on GitHub issues or pull requests should add content to the discussions. 
+Approbation comments such as *+1* or *I would like this feature to be implemented as well* will be deleted by the maintainers. Please use [GitHub reactions](https://github.com/blog/2119-add-reactions-to-pull-requests-issues-and-comments) instead.
 
 ## Issue labels