[DisplayText] Split up medium and large display text (#2100)

* Splitting up medium and large display text

* Updating content based on feedback

* Added changelog entry

Author: jkeussen

UNRELEASED.md

@@ -16,3 +16,4 @@ Use [the changelog guidelines](https://git.io/polaris-changelog-guidelines) to f
 ### Documentation
 
 - Updated banner guidelines to make it clearer when success banners should be used vs success toasts. ([#2046](https://github.com/Shopify/polaris-react/pull/2046))
+- Updated display text documentation to have a separate example for medium and large display

src/components/DisplayText/README.md

@@ -90,9 +90,17 @@ Use this size sparingly and never multiple times on the same page.
 
 <!-- /content-for -->
 
-### Medium and large
+### Large
 
-Use as part of complex data displays to highlight key numbers, or to harmonize with other display text.
+Use for display text that’s more important than the medium size, but less important than extra large.
+
+```jsx
+<DisplayText size="large">Good evening, Dominic.</DisplayText>
+```
+
+### Medium
+
+Use for display text that’s more important than the small size, but less important than large.
 
 ```jsx
 <DisplayText size="medium">Good evening, Dominic.</DisplayText>