Add Readability scores to vale.

Author: samcunliffe

.vale.ini

@@ -2,12 +2,14 @@ StylesPath = .github/styles
 
 # https://github.com/errata-ai/packages
 Packages = proselint,\
-           write-good
+           write-good,\
+           Readability
 
 [*.md]
 BasedOnStyles = proselint,\
                 Vale,\
-                write-good
+                write-good,\
+                Readability
 
 # Disable
 Vale.Spelling = NO