Add introduction

rules/S7172/cfamily/rule.adoc

@@ -1,3 +1,4 @@
+This rule raises an issue when `std::optional`, `boost::optional`, or `std::expected` wrap a basic type, and a conversion from the wrapper type to `bool` is used to test the presence of a contained value.
 
 == Why is this an issue?
 
@@ -13,7 +14,7 @@ if(flag.has_value()) { ... }
 
 When the contained type is also convertible to `bool`, using this concise syntax can be confusing. What is tested: The wrapper, or the contained value?
 
-This rule raises an issue when `std::optional`, `boost::optional`, or `std::expected` wrap a basic type, and the conversion to `bool` is used to test presence of the value.
+This rule raises an issue when `std::optional`, `boost::optional`, or `std::expected` wrap a basic type, and the conversion to `bool` is used to test the presence of the value.
 
 === What is the potential impact?