Link to graphfunctions in readme is broken

[AaldertVanWijk-TomTom]

scalyr-grafana-datasource-plugin/README.md

Line 98 in dd247de

[This](https://www.scalyr.com/help/dashboards#graphFunctions) is a good

I'm trying to write some expressions for this plugin but I cannot find a list of supported functions. The link in the README is sadly broken

[weilliu]

@AaldertVanWijk-TomTom Sorry about that. The correct URL is https://app.scalyr.com/help/dashboards?#graphFunctions
I will file a documentation ticket to fix the links. For now, please replace www.scalyr.com with app.scalyr.com to access the page you need.