docs(readme): Updated axe-core coverage number (#2908)

README.md

@@ -16,7 +16,7 @@ Axe is an accessibility testing engine for websites and other HTML-based user in
 
 Axe-core has different types of rules, for WCAG 2.0 and 2.1 on level A and AA, as well as a number of best practices that help you identify common accessibility practices like ensuring every page has an `h1` heading, and to help you avoid "gotchas" in ARIA like where an ARIA attribute you used will get ignored.
 
-With axe-core, you can find **up to 50% of WCAG issues automatically**. Additionally, axe-core will return elements as "incomplete" where axe-core could not be certain, and manual review is needed. To further improve test coverage we recommend the [intelligent guided tests](https://www.youtube.com/watch?v=AtsX0dPCG_4&feature=youtu.be&ab_channel=DequeSystems) in the [axe Extension](https://www.deque.com/axe/browser-extensions/).
+With axe-core, you can find **on average 57% of WCAG issues automatically**. Additionally, axe-core will return elements as "incomplete" where axe-core could not be certain, and manual review is needed. To further improve test coverage we recommend the [intelligent guided tests](https://www.youtube.com/watch?v=AtsX0dPCG_4&feature=youtu.be&ab_channel=DequeSystems) in the [axe Extension](https://www.deque.com/axe/browser-extensions/).
 
 The complete list of rules, grouped WCAG level and best practice, can found in [doc/rule-descriptions.md](./doc/rule-descriptions.md).