Updated due to discussion about #1068

CppCoreGuidelines.md

@@ -1190,7 +1190,7 @@ Having good (easy-to-understand, encouraging efficient use, not error-prone, sup
 Interface rule summary:
 
 * [I.1: Make interfaces explicit](#Ri-explicit)
-* [I.2: Avoid global variables](#Ri-global)
+* [I.2: Avoid non-`const` global variables](#Ri-global)
 * [I.3: Avoid singletons](#Ri-singleton)
 * [I.4: Make interfaces precisely and strongly typed](#Ri-typed)
 * [I.5: State preconditions (if any)](#Ri-pre)
@@ -1264,7 +1264,7 @@ Functions can be template functions and sets of functions can be classes or clas
 * (Simple) A function should not make control-flow decisions based on the values of variables declared at namespace scope.
 * (Simple) A function should not write to variables declared at namespace scope.
 
-### <a name="Ri-global"></a>I.2: Avoid global variables
+### <a name="Ri-global"></a>I.2: Avoid non-`const` global variables
 
 ##### Reason