Clarify that can is sometimes a valid verb for predicate names

Author: dvandersluis

README.adoc

@@ -1047,9 +1047,11 @@ end
 
 === Predicate Methods Prefix [[bool-methods-prefix]]
 
-Avoid prefixing predicate methods with the auxiliary verbs such as `is`, `does`, or `can`.
+Avoid prefixing predicate methods with the auxiliary verbs such as `is`, `has` or `does`.
 These words are redundant and inconsistent with the style of boolean methods in the Ruby core library, such as `empty?` and `include?`.
 
+NOTE: `can` should also be avoided when possible, but is also useful when meaning "allowed to".
+
 [source,ruby]
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 # bad