Googletest export

Fix a link to the guide for creating custom matchers.

PiperOrigin-RevId: 262572684

googlemock/docs/for_dummies.md

@@ -375,7 +375,7 @@ In the above examples, `100` and `50` are also matchers; implicitly, they are
 the same as `Eq(100)` and `Eq(50)`, which specify that the argument must be
 equal (using `operator==`) to the matcher argument. There are many
 [built-in matchers](#MatcherList) for common types (as well as
-[custom matchers](#NewMatchers)); for example:
+[custom matchers](cook_book.md#NewMatchers)); for example:
 
 ```cpp
 using ::testing::Ge;