Clarify minimum Chrome 64 (run) / Chrome 80 (open) (#5891)

docs/guides/guides/launching-browsers.mdx

@@ -49,7 +49,7 @@ browser by using the drop down near the top right corner:
 
 Cypress supports the browser versions below:
 
-- Chrome 80 and above.
+- Chrome 64 and above. Chrome 80 and above is required for `cypress open` usage.
 - Edge 80 and above.
 - Firefox 86 and above.
 
@@ -85,7 +85,8 @@ seeing failures in CI, to easily debug them you may want to run locally with the
 ### Chrome Browsers
 
 All Chrome\* flavored browsers will be detected and are supported above
-Chrome 64.
+Chrome 64, with the restriction that a minimum of Chrome 80 is required to use
+`cypress open`.
 
 You can launch Chrome like this: