Add documentation for contrib/limit_depth.hpp

Author: d-frey

doc/Contrib-and-Examples.md

@@ -40,6 +40,12 @@ For all questions and remarks contact us at **taocpp(at)icemx.net**.
 
 * Grammars and actions for PEGTL-input-to-integer conversions.
 
+###### `<tao/pegtl/contrib/limit_depth.hpp>`
+
+* Limits the nesting level of rules when parsing a grammar, prevents stack overflows.
+* Can be applied selectively at specific rules to improve efficiency.
+* See `src/test/pegtl/limit_depth.cpp`.
+
 ###### `<tao/pegtl/contrib/json.hpp>`
 
 * JSON grammar according to [RFC 7159](https://tools.ietf.org/html/rfc7159) (for UTF-8 encoded JSON only).