Update README with current Styleguide links (#62)

Updated our Styleguide link to:
* match the latest guidance our UX Designer Ciaran added to Zeplin
* to call our Carbon as our meta-guide
* to point people to the overrides folder

packages/esm-styleguide/README.md

@@ -2,7 +2,10 @@
 
 The styleguide for OpenMRS.
 
-Please see [styleguide.openmrs.org](http://styleguide.openmrs.org/)
+All our frontend UI development is based on [Carbon Design System](https://www.carbondesignsystem.com/). 
+
+Please see [our latest styleguide here](https://app.zeplin.io/project/5f7223cfda10f94d67cec6d0/styleguide/components/). 
+Nuanced overrides of Carbon are specifically highlighted in [/src/carbon-overrides.css](https://github.com/openmrs/openmrs-esm-core/blob/master/packages/esm-styleguide/src/carbon-overrides.css).
 
 ## Contributing / Development